diag: Change implementation of diag log masks

Currently, the structure of diag log masks can lead to buffer
corruption when there is huge different between the log masks
of the Apss processor and the peripherals. Make changes to
log masks to be of constant size.

Change-Id: I9920bbcc19e75c10ec7267808c9fc4afaafeff5b
CRs-Fixed: 556401
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>