The RTL9300/RTL9310 I2C controllers have support for 2 independent I2C
masters, each with a fixed SCL pin, that cannot be changed. Each of these
masters can use 8 (RTL9300) or 16 (RTL9310) different pins for SDA.
This multiplexer directly controls the two masters and their shared
IO configuration registers to allow multiplexing between any of these
busses. The two masters cannot be used in parallel as the multiplex
is protected by a standard multiplex lock.

Signed-off-by: Birger Koblitz <git@birger-koblitz.de>