arm64: dts: imx8mq-evk: VDD_ARM power rail is always ON

On i.MX8MQ EVK board, VDD_ARM is from a DC-DC converter which
is always ON, the GPIO1_IO13 is ONLY to switch VDD_ARM's voltage
between 0.9V and 1V for CPU DVFS, so VDD_ARM's GPIO regulator
should be always ON to avoid below confusion after kernel boot
up:

imx8mqevk login:
[   31.776619] vdd_arm: disabling

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>