msm: kgsl: Add function to check internal commands

This check is in multiple places, so make an inline
function for better code readability. Also, rename
the function to reflect its true intention.

Change-Id: I8172200ee70d670c656c28786b37912b574c6c00
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>