arm: am33xx: add TSC/ADC mfd device support

Add support for core multifunctional device along
with its clients touchscreen and ADC.

Signed-off-by: Pantelis Antoniou <panto@antoniou-consulting.com>
Signed-off-by: Patil, Rachna <rachna@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>