board: sl28: print CPLD version on bootup

Most of the time it is very useful to have the version of the board
management controller. Now that we have a driver, print it during
startup.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>

misc: add sl28cpld base driver

Add a multi-function device driver which will probe its children and
provides methods to access the device.

Signed-off-by: Michael Walle <michael@walle.cc>
[Rebased]
Signed-off-by: Priyanka Jain <priyanka.jain@nxp.com>