msm: ocmem: Serialize allocation requests only when necessary

Certain clients of ocmem always have exclusive regions set aside in
the OCMEM memory map. Allocation requests for such clients do not
have to wait for any pending evictions in progress to be completed
nor will trigger any new evictions and can be safely scheduled right
away.

CRs-Fixed: 599002
Change-Id: I54369bca9d26378a9aa70db83d35ab94866a3ff1
Signed-off-by: Naveen Ramaraj <nramaraj@codeaurora.org>
Signed-off-by: Neeti Desai <neetid@codeaurora.org>