ARM: imx: Force DRAM regulators into FPWM mode on DH i.MX8MP DHCOM SoM

In case the Buck5 and Buck6 regulators which supply DRAM Vdd1 and Vdd2/Vddq
respectively operate in automatic PWM/PFM mode, the DRAM EDAC detects more
correctable errors than if the regulators operate in forced PWM only mode.
Force DRAM regulators to forced PWM mode only to stop tempting the DRAM.

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