ARM: dts: am437x-idk-evm: Disable OPP50 for MPU

AM437x IDK has a TPS386000 supply voltage supervisor on the VDD_MPU rail
set to trigger undervoltage condition at 0.96V. Because of this, OPP50,
which is normally configured to 300MHz at 0.95V, must be disabled to
avoid triggering the undervoltage condition. Also mark OPP100 as the
suspend-opp as it is now our lowest OPP.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>