msm: kgsl: Purge reallocated addresses from the free mem list

Purge memory addresses that got quickly reallocated from the freed
memory list so they don't serve as red herrings if a pagefault
occurs with the newly reallocated buffer.

Change-Id: Ic0dedbada0090d54d4c6bf3a4485c35883240d44
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>