Add new ioctls for per context timestamps.
Timestamp functions (read/write/wait) will now be context
specific rather than only using the global timestamp.
Per context timestamps is a requirement for priority
based queueing.
Userspace will set a flag in the context if preambles are in use. If
they are, we can safely skip save and restore commands for the
context. GMEM save/restore is still required. To improve performance,
preamble commands are skipped when the context hasn't changed since
the last issueibcmds.
from Code Aurora
