Start collecting all the FB plane related functions into a new intel_fb.c
file.

v2: Drop display/ part of header includes. (Ville)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210325214808.2071517-7-imre.deak@intel.com