drm/i915: Move is_ccs_modifier() to intel_fb.c

Move the function to intel_fb.c and rename it adding the intel_fb_
prefix following the naming of exported functions.

Cc: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211020195138.1841242-11-imre.deak@intel.com