pvr: Check if the buffer/image was bound before unbinding.

Signed-off-by: Rajnesh Kanwal <rajnesh.kanwal@imgtec.com>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Part-of: <!15641>
35 jobs for !15641 with dev/fix_buffer_image_unbinding/base in 7 minutes and 32 seconds (queued for 2 seconds)
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