media: i2c: ds90ub960: Add support for I2C_RX_ID

media: i2c: ds90ub960: Add support for I2C_RX_ID

Normally the driver accesses both the RX and the TX port registers via a
paging mechanism: one register is used to select the page (i.e. the
port), which dictates the port used when accessing the port specific
registers.

The downside to this is that while debugging it's almost impossible to
access the port specific registers from the userspace, as the driver can
change the page at any moment.

The hardware supports another access mechanism: using the I2C_RX_ID
registers (one for each RX port), i2c addresses can be chosen which,
when accessed, will always use the specific port's registers, skipping
the paging mechanism.

The support is only for the RX port, but it has proven very handy while
debugging and testing. So let's add the code for this, but hide it
behind a disabled define.

Reviewed-by: Jai Luthra <jai.luthra@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>