ARM: dts: AM437X-GP-EVM: AM437X-SK-EVM: Make dcdc3 dcdc5 and dcdc6 enable during suspend

dcdc3, dcdc5, dcdc6 supply ddr and rtc respectively. These
are required to be on during suspend. Hence set the state accordingly.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>