gpu: pvr: pdumpfs: add initial frame handling and debugfs support

gpu: pvr: pdumpfs: add initial frame handling and debugfs support

This adds the separate handling of the initial frame, and adds
debugfs support for this initial frame.

The initial frame is the frame started when the driver is initialised.
Once userspace flags the first frame, the initial frame is ended, and
a new frame started, but the initial frame is not part of the stream
list. The initial frame therefor does not get culled as part of
standard frame culling and is kept around for the life of the driver.

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