Move the function retrieving the format override information for a given
format/modifier to intel_fb.c. We can store a pointer to the format list
in each modifier's descriptor instead of the corresponding switch/case
logic, avoiding the listing of the modifiers twice.

v1: Unchanged.
v2: Handle invalid modifiers in intel_fb_get_format_info() passed from
    userspace. (CI/igt_kms_addfb_basic/addfb25-bad-modifier)
v3: Move lookup_modifier() to the next patch, where it's first used.

Cc: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.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/20211020195138.1841242-3-imre.deak@intel.com