i2c: muxes: pca954x: add PCA9847 variant

This seems to be very similar to the already existing PCA9547, save for
the fact that it supports 0.8V and doesn't support 5V. In fact, it is so
similar to the PCA9547 that the NXP LS1028A-RDB board has been driving
this chip using a "nxp,pca9547" compatible string.

Create a new compatible for the PCA9847 (which is the same as in Linux)
and define the same operating parameters for it as for PCA9547.

Cc: Heiko Schocher <hs@denx.de>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
Reviewed-by: Michael Walle <michael@walle.cc>