drm/v3d: Size the kperfmon_ids array at runtime

Instead of statically reserving pessimistic space for the kperfmon_ids
array, make the userspace extension code allocate the exactly required
amount of space.

Apart from saving some memory at runtime, this also removes the need for
the V3D_MAX_PERFMONS macro whose removal will benefit further driver
cleanup.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240711135340.84617-8-tursulin@igalia.com