drm/amd/display: make FBC configurable option

Currently FBC is guarded with ENABLE_FBC macro,
which needs to be manually enabled in Makefile.

This patch moves it to Kconfig so that there
wont be any need to additional patch to be carried
for enabling or disabling on every SoC.

Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Roman Li <Roman.Li@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>