gpu: pvr: pdumpfs: add frame struct and initial frame handling code

gpu: pvr: pdumpfs: add frame struct and initial frame handling code

Now we are tracking frames correctly, but we are not accepting any data
yet. frame_current is the last of frame_stream, and the frame that we
would be writing to.

New frames are created when userspace flags the start of a new frame
with PDumpSetFrameKM. This is also where we deliberately change the
pdump content by adding two comments. One for flagging the end of the
previous frame, one for the start of the new frame.

We keep at most frame_count_max frames around, older frames will be
removed by frame_cull() which gets called when a new frame gets
created.

Signed-off-by: Luc Verhaegen <libv@codethink.co.uk>
Signed-off-by: Imre Deak <imre.deak@nokia.com>