msm: kgsl: Protect the memdesc->gpuaddr in SVM use cases

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



When SVM is being used there can only be one GPU address assigned
to the memory descriptor. Don't allow the GPU address to be changed
after it has been negotiated the first time by a process.

Change-Id: Ic0dedbad2a1b3ccdc2c1598a6c501b2be288d64e
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Harshitha Sai Neelati <hsaine@codeaurora.org>
Signed-off-by: Archana Sriram <apsrir@codeaurora.org>
(cherry picked from commit 2ea97829329493c4614df70b27411b11d4d5ed75)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>