linux-firmware: add packages for Qualcomm XElite GPU firmware

Add two packages to handle Qualcomm XElite firmware, one for the
board-specific signed blob and one for the unsigned (generic) GPU
firmware files.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>