drm/radeon: restructure edid fetching

Split radeon_ddc_get_modes() and move it into
radeon_connectors.c since that is the only place
that uses it.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --cc drivers/gpu/drm/radeon/radeon_connectors.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_display.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_mode.h
Simple merge