msm: kgsl: Support the KGSL_CONTEXT_CTX_SWITCH flag

Sometimes the user driver has reason to force the command preamble
to run on every submit and not just when the context is switched.
Support KGSL_CONTEXT_CTX_SWITCH for both an entire context or
just a single submission.

Change-Id: Ic0dedbad52fae5fd6ca975ea7eb9f1002e0815ed
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>