imx: Add support for Ronetix's iMX7-CM board

Console boot log:

U-Boot SPL 2021.04-00836-ga6232e065d-dirty (Apr 16 2021 - 15:16:35 +0200)
Trying to boot from MMC1

U-Boot 2021.04-00836-ga6232e065d-dirty (Apr 16 2021 - 15:16:35 +0200)

CPU:   Freescale i.MX7D rev1.3 1000 MHz (running at 792 MHz)
CPU:   Commercial temperature grade (0C to 95C) at 44C
Reset cause: POR
Model: Ronetix iMX7-CM Board
Board: iMX7-CM
DRAM:  512 MiB
PMIC:  PFUZE3000 DEV_ID=0x30 REV_ID=0x11
MMC:   FSL_SDHC: 0, FSL_SDHC: 2
Loading Environment from MMC... OK
In:    serial
Out:   serial
Err:   serial
Net:
Warning: ethernet@30be0000 (eth0) using random MAC address - fe:be:37:01:5a:3f
eth0: ethernet@30be0000
Hit any key to stop autoboot:  0

Signed-off-by: Ilko Iliev <iliev@ronetix.at>