media: ti-vpe: cal: Simplify the context API

Rework the context API exposed to cal-video.c to simplify it. The
configuration and enable steps are all grouped in a single
cal_ctx_start() function, and the DMA stop and IRQ disable are similarly
groupd in cal_ctx_stop(). The cal_ctx_wr_dma_addr() function is renamed
to cal_ctx_set_dma_addr() for consistency with the cal_ctx_ prefix of
the start and stop functions.

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>