drm/panfrost: Clamp lock region to Bifrost minimum

When locking a region, we currently clamp to a PAGE_SIZE as the minimum
lock region. While this is valid for Midgard, it is invalid for Bifrost,
where the minimum locking size is 8x larger than the 4k page size. Add a
hardware definition for the minimum lock region size (corresponding to
KBASE_LOCK_REGION_MIN_SIZE_LOG2 in kbase) and respect it.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Tested-by: Chris Morgan <macromorgan@hotmail.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210824173028.7528-4-alyssa.rosenzweig@collabora.com