i2c: Zynq: Support for TI PCA9548 bus multiplexer

(Interface is not quite the same as Phillips PCA9547.)

Signed-off-by: Michael Burr <michael.burr@logicpd.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Michal Simek <monstr@monstr.eu>