msm: kgsl: Do not reclaim pages mapped in a VBO

Pages mapped into a VBO can be accessible both through the memdesc as well
as through the parent VBO. Reclaiming these pages would require a lot of
overhead to update iommu mappings. Instead, do not reclaim the pages of a
memdesc that is currently mapped in a VBO.

Change-Id: Ic2787f09081c5dc3a66c3582b98266937c8ce1e5
Signed-off-by: Lynus Vaz <[email protected]>
Signed-off-by: Sanjay Yadav <[email protected]>