ARM: dts: dra7-evm: Rename evm_3v3 regulator to vsys_3v3

On the new schematics it is renamed and the same name is used on other
dra7 boards.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>