util: Add a drm_find_modifier helper

util: Add a drm_find_modifier helper

This function is replicated across vc4/v3d/freedreno and is needed in
Panfrost; let's make this shared code.

v2: Supply generic util_array_contains_u64 version (Eric Engestrom). Add
missing stdbool.h include (Eric Anholt). Mark inline (Christian
Gmeiner).

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>