diag: Synchronize msg mask read and write on a peripheral

The patch synchronizes msg mask read and write on a peripheral
by proper protection of mask_info and msg_mask_table_count.

CRs-Fixed: 2042362, 2055291
Change-Id: If136012855834b0b8cba91eb66bf711750e8f372
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>