ocmem: Add debugfs node to track latency for ocmem

Add new node "timing" to measure the time taken by the
ocmem driver during allocation and freeing of ocmem memory
for each of the clients.

Change-Id: Ib901c6f4cad35430da97f898a37645206ffc881f
Signed-off-by: Neeti Desai <neetid@codeaurora.org>