msm: kgsl: clean up context flags and priv bits

Move adreno_context.priv values into the top half of
kgsl_context.priv, because there's no reason to have multiple
sets of priv bits wandering around.

Change ADRENO_CONTEXT_STATE_INVALID into a priv bit, so that
it works more like DETACHED.

Change-Id: Ie5a4bc3b9dcede78047bf7b5f67ddcc39cf1dd3e
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>