Key frame non-RD mode decision process

This commit makes a non-RD coding mode decision process for key
frame coding. It can be optionally turned on in speed -6 and above.

Change-Id: I0847258b392877a0210b4768bef88ebc9ad009b5
Refactored idct routines and headers

This change is made in preparation for a
subsequent patch which adds acceleration
for the highbitdepth transform functions.

The highbitdepth transform functions attempt
to use 16/32bit sse instructions where possible,
but fallback to using the C implementations if
potential overflow is detected.  For this reason
the dct routines are made global so they can be
called from the acceleration functions in the
subsequent patch.

Change-Id: Ia921f191bf6936ccba4f13e8461624b120c1f665
(cherry picked from commit 454342d4e77dbb67f4a3c10f97a57a6fcb46d9a0)
Merge "Refactored idct routines and headers"
Merge "Key frame non-RD mode decision process"