bus: ti-sysc: Support 16-bit writes too

We need to also support 16-bit writes for i2c in addition to the reads
when we start configuring the sysconfig register for reset and idle modes.

Note that only i2c revision register has LO and HI registers, so let's
add a check also for 16-bit register read. This change is currently cosmetic
and does not affect anything until we enable the module specific quirk
handling for i2c reset and enable later on.

Signed-off-by: Tony Lindgren <tony@atomide.com>