Add support for TI TPS53676 controller to the tps53679 pmbus driver

The driver uses the USER_DATA_03 register to figure out how many phases
are enabled and to which channel they are assigned, and sets the number
of pages and phases accordingly.
Signed-off-by: Erik Rosen <erik.rosen@metormote.com>
Link: https://lore.kernel.org/r/20210322193734.75127-3-erik.rosen@metormote.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>