msm: Fix mem leak when using per-process pages

When GPU is using per process page tables the code creates
a new page table (domain) for every process. There is also
some associated structures allocated to keep track of each
domain. However, when cleaning up the memory used for a page
table only the domain is freed and not the associated structures.

Add a function to allow a client to properly unregister a domain
which will free all the memory associated with a domain.
Call the unregister function from kgsl driver code.

CRs-fixed: 480801
Change-Id: I9704c12c66a95ce66cea63b619bbdbafa0f1eac8
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>