platform: Add Surface platform directory

platform: Add Surface platform directory

It may make sense to split the Microsoft Surface hardware platform
drivers out to a separate subdirectory, since some of it may be shared
between ARM and x86 in the future (regarding devices like the Surface
Pro X).

Further, newer Surface devices will require additional platform drivers
for fundamental support (mostly regarding their embedded controller),
which may also warrant this split from a size perspective.

This commit introduces a new platform/surface subdirectory for the
Surface device family, with subsequent commits moving existing Surface
drivers over from platform/x86.

A new MAINTAINERS entry is added for this directory. Patches to files in
this directory will be taken up by the platform-drivers-x86 team (i.e.
Hans de Goede and Mark Gross) after they have been reviewed by
Maximilian Luz.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20201009141128.683254-2-luzmaximilian@gmail.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>