drm/imagination: Hold drm_gem_gpuva lock for unmap

Avoid a warning from drm_gem_gpuva_assert_lock_held in drm_gpuva_unlink.

The Imagination driver uses the GEM object reservation lock to protect
the gpuva list, but the GEM object was not always known in the code
paths that ended up calling drm_gpuva_unlink. When the GEM object isn't
known, it is found by calling drm_gpuva_find to lookup the object
associated with a given virtual address range, or by calling
drm_gpuva_find_first when removing all mappings.

Cc: stable@vger.kernel.org
Fixes: 4bc736f8 ("drm/imagination: vm: make use of GPUVM's drm_exec helper")
Signed-off-by: Brendan King <brendan.king@imgtec.com>
Reviewed-by: Matt Coster <matt.coster@imgtec.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250226-hold-drm_gem_gpuva-lock-for-unmap-v2-1-3fdacded227f@imgtec.com


Signed-off-by: Matt Coster <matt.coster@imgtec.com>