drm/radeon,amdgpu,dc: enable ABGR and XBGR formats

[Mauro Rossi]

Sending a respin for support of {A,X}RGB pixel formats in DCE1 and later,
with separate patches for amd dc, amdgpu and radeon

Please review taking in to account following doubts I have:

For amd dc crossbars register controls to swap red and blue channels
are already implemented in drm/amd/display/dc/dce/dce_mem_input.c
Do we need them also in dce 8, 10, 11 modules?

For amdgpu: What are the necessary *_reg.h header to consider for 
crossbars register controls in amdgpu in order to cover all parts
(si, cik and later) with amd dc disabled?

[PATCH v2 1/3] drm/amd/display: enable ABGR and XBGR formats (v3)
[PATCH v2 2/3] drm/amdgpu: enable enable ABGR and XBGR formats
[PATCH v2 3/3] drm/radeon: enable ABGR and XBGR formats