ath9k_htc: introduce support for different fw versions

ath9k_htc: introduce support for different fw versions

Current kernel support only one fw name with theoretically only one
fw version located in “firmware/htc_[9271|7010].fw”. Which is ok so far we
have only one fw version (1.3). After we realised new fw 1.4, we faced
compatibility problem which was decided to solve by firmware name and
location:
- new firmware is located now in
	firmware/ath9k_htc/htc_[9271|7010]-1.4.0.fw
- old version 1.3 should be on old place, so old kernel have no issues
	with it.
- new kernels including this patch should be able to try different
	supported (min..max) fw version.
- new kernel should be able to support old fw location too. At least for
	now.

At same time this patch will add new module option which should allow user
to play with development  fw version without replacing stable one. If user
will set “ath9k_htc use_dev_fw=1” module will try to find
firmware/ath9k_htc/htc_[9271|7010]-1.dev.0.fw first and if it fails, use
stable version: for example...1.4.0.fw.

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>