arm64: dts: imx8mp: Make GPIO3 available early in U-Boot proper on i.MX8MP DHCOM

The GPIO3 has to be available early during U-Boot proper start up for
DRAM size detect to work correctly. The GPIO3 is currently available in
SPL and late in U-Boot proper, which is insufficient. Add the missing
bootph-all to make the GPIO3 available also early in U-Boot proper.

Signed-off-by: Marek Vasut <marex@denx.de>