drm/panfrost: Remove unused id_mask from struct panfrost_model

drm/panfrost: Remove unused id_mask from struct panfrost_model

[ Upstream commit 581d1f8248550f2b67847e6d84f29fbe3751ea0a ]

The id_mask field of struct panfrost_model has never been used.

Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver")
Signed-off-by: Steven Price <steven.price@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241025140008.385081-1-steven.price@arm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>