media: ti-vpe: cal: Fold PPI enable in CAMERARX .s_stream()

To further decouple the context and CAMERARX components, move the call
to cal_camerarx_ppi_enable() from cal_start_streaming() to the CAMERARX
.s_stream() operation. The DMA destination address has to be set before
starting the CAMERARX, which is desirable anyway.

cal_camerarx_ppi_disable() will be addressed separately.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>