ARM: dts: dra72-evm-common: Correct vmmc-supply for mmc2

On dra72/dra71 evms, mmc2 vdd/ios are connected to a common 1.8V supply
not 3.3V. Also the regulator that supplies 1.8V is different on dra71-evm
so move the supply property from common dtsi to evm specific dts files.

Fixes: a4240d3a ("ARM: dts: Add support for dra72-evm rev C (SR2.0)")
Signed-off-by: Ravikumar Kattekola <rk@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>