msm: kgsl: Add secure memory flag in process mem file

Secure memory will have 's' flag set in its flag fields.
This is needed to track secure memory of a process.

CRs-Fixed: 985767
Change-Id: I011dcc951b1db8adf763f85701aa869f6d4744d3
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>