drm: Add HDMI infoframe helpers

Add a generic helper to fill in an HDMI AVI infoframe with data
extracted from a DRM display mode.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/Kconfig

@@ -7,6 +7,7 @@
 menuconfig DRM
 	tristate "Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)"
 	depends on (AGP || AGP=n) && !EMULATED_CMPXCHG && MMU
+	select HDMI
 	select I2C
 	select I2C_ALGOBIT
 	select DMA_SHARED_BUFFER