mfd: Add companion chip in 88pm80x

in hw design, 800 is mainly for pmic control, while 805 for audio.
but there are 3 registers which controls class D speaker property,
and they are defined in 800 i2c client domain. so 805 codec driver
needs to use 800 i2c client to access class D speaker reg for
audio path management. so add this workaround for the purpose to
let 805 access 800 i2c in some scenario.

Signed-off-by: Qiao Zhou <zhouqiao@marvell.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>