drm/vc4: Replace IDR with XArray for perfmon tracking

drm/vc4: Replace IDR with XArray for perfmon tracking

The IDR interface is deprecated and the XArray API is the recommended
replacement. Replace the per-file IDR used to track perfmons with an
XArray. This allows us to remove the external mutex that protects the
IDR.

While at it, introduce the vc4_perfmon_delete() helper to consolidate
the perfmon cleanup logic used by both vc4_perfmon_close_file() and
vc4_perfmon_destroy_ioctl(). Also, remove the redundant assignment of
vc4file->dev to itself in vc4_perfmon_open_file().

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Link: https://patch.msgid.link/20260127115822.64401-2-mcanal@igalia.com
Signed-off-by: Maíra Canal <mcanal@igalia.com>