msm: vidc: Add control to preserve text quality

V4L2_CID_MPEG_VIDC_VIDEO_PRESERVE_TEXT_QUALITY allows the client to
tell the encoder to preserve the text quality whenever a given frame
contains text elements.  This reduces the amount of artifacts around the
text in the encoded frame.

Change-Id: If75ea580adaedc896d8a31410a194076f38b5179
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>