media: imx-jpeg: Remove soft reset between frames encoding

Remove soft reset between frames, which was merely a workaround,
actually replace it with something less aggressive: clearing of jpeg stream
buffer pointer, via STM_CTRL[BITBUF_PTR_CLR].
According to the reference manual, the BITBUF_PTR_CLR is performed on
context switch, but, per hardware team recommendation, it is also working
without context switch, which is the case for this driver, for now.

Without soft reset and without BITBUF_PTR_CLR, successive encoding jobs
continue from where the previous left off, basically writing past the
v4l2 buffer.

Signed-off-by: Mirela Rabulea <mirela.rabulea@nxp.com>
Reviewed-by: Robert Chiras <robert.chiras@nxp.com>
Reviewed-by: Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>