drm/i915: Include asm sources for {ivb, hsw}_clear_kernel.c

drm/i915: Include asm sources for {ivb, hsw}_clear_kernel.c

Alexandre Oliva has recently removed these files from Linux Libre
with concerns that the sources weren't available.

The sources are available on IGT repository, and only open source
tools are used to generate the {ivb,hsw}_clear_kernel.c files.

However, the remaining concern from Alexandre Oliva was around
GPL license and the source not been present when distributing
the code.

So, it looks like 2 alternatives are possible, the use of
linux-firmware.git repository to store the blob or making sure
that the source is also present in our tree. Since the goal
is to limit the i915 firmware to only the micro-controller blobs
let's make sure that we do include the asm sources here in our tree.

Btw, I tried to have some diligence here and make sure that the
asms that these commits are adding are truly the source for
the mentioned files:

igt$ ./scripts/generate_clear_kernel.sh -g ivb \
     -m ~/mesa/build/src/intel/tools/i965_asm
Output file not specified - using default file "ivb-cb_assembled"

Generating gen7 CB Kernel assembled file "ivb_clear_kernel.c"
for i915 driver...

igt$ diff ~/i915/drm-tip/drivers/gpu/drm/i915/gt/ivb_clear_kernel.c \
     ivb_clear_kernel.c

<  * Generated by: IGT Gpu Tools on Fri 21 Feb 2020 05:29:32 AM UTC
>  * Generated by: IGT Gpu Tools on Mon 08 Jun 2020 10:00:54 AM PDT
61c61
< };
> };
\ No newline at end of file

igt$ ./scripts/generate_clear_kernel.sh -g hsw \
     -m ~/mesa/build/src/intel/tools/i965_asm
Output file not specified - using default file "hsw-cb_assembled"

Generating gen7.5 CB Kernel assembled file "hsw_clear_kernel.c"
for i915 driver...

igt$ diff ~/i915/drm-tip/drivers/gpu/drm/i915/gt/hsw_clear_kernel.c \
     hsw_clear_kernel.c
5c5
<  * Generated by: IGT Gpu Tools on Fri 21 Feb 2020 05:30:13 AM UTC
>  * Generated by: IGT Gpu Tools on Mon 08 Jun 2020 10:01:42 AM PDT
61c61
< };
> };
\ No newline at end of file

Used IGT and Mesa master repositories from Fri Jun 5 2020)
IGT: 53e8c878a6fb ("tests/kms_chamelium: Force reprobe after replugging
     the connector")
Mesa: 5d13c7477eb1 ("radv: set keep_statistic_info with
      RADV_DEBUG=shaderstats")
Mesa built with: meson build -D platforms=drm,x11 -D dri-drivers=i965 \
                 -D gallium-drivers=iris -D prefix=/usr \
		 -D libdir=/usr/lib64/ -Dtools=intel \
		 -Dkulkan-drivers=intel && ninja -C build

v2: Header clean-up and include build instructions in a readme (Chris)
    Modified commit message to respect check-patch

Reference: http://www.fsfla.org/pipermail/linux-libre/2020-June/003374.html
Reference: http://www.fsfla.org/pipermail/linux-libre/2020-June/003375.html
Fixes: 47f8253d2b89 ("drm/i915/gen7: Clear all EU/L3 residual contexts")
Cc: <stable@vger.kernel.org> # v5.7+
Cc: Alexandre Oliva <lxoliva@fsfla.org>
Cc: Prathap Kumar Valsan <prathap.kumar.valsan@intel.com>
Cc: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Jon Bloomfield <jon.bloomfield@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200610201807.191440-1-rodrigo.vivi@intel.com
(cherry picked from commit 5a7eeb8ba143d860050ecea924a8f074f02d8023)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>