To prepare for the split of the camerarx code to a separate file, move
the CAL I/O accessors to cal.h. This requires renaming the accessors
with a cal_prefix, as the current names are too generic and prone to
namespace clashes.

The reg_read() and read_write() macros, that cover both CAL and CAMERARX
register access, are split in two groups of inline functions, one for
CAL access and one for CAMERARX access.
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>