msm: kgsl: Don't allow re-importing memory owned by KGSL

BugLink: https://bugs.launchpad.net/bugs/1931727



Don't allow IOCTL_KGSL_MAP_USER_MEM to import user memory that was
already allocated and mapped by KGSL in the first place.  Remapping
memory never makes sense and it messes up reference counting in the
pools.

Change-Id: Ic0dedbade96ac6b30dcbbb794bf57a597f1bb351
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Pankaj Gupta <gpankaj@codeaurora.org>
(cherry picked from commit 9997d34171f3d133ae3816ce840c0ab9fc4c2232)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>