msm: kgsl: Omit secure mode packets for context switching

Currently, the secure mode packets will be inserted around the
pagetable switch packets if the last active context was secure.
Fix this to never insert secure mode packets for pagetable switch
or internal commands.

Change-Id: I39283b18d758cbacf7012aea63375543b6c73b4c
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>