drm/nouveau/gk20a: Add MODULE_FIRMWARE for gk20a

This patch is needed by initramfs tools to detect
the required firmware files for the module.

This patch tests for either TEGRA_124_SOC or TEGRA_132_SOC
for the firmwares related to the Tegra K1 generation.

v2: move the MODULE_FIRMWARE to the nvidia_platform.c file.
 This will avoid to test for NOUVEAU_PLATFORM_DRIVER

Signed-off-by: Nicolas Chauvet <kwizart@gmail.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>