imx: support i.MX8QM ROM 7720 a1 board

Add i.MX8QM ROM 7720a1 board support

Boot log as below:
U-Boot 2019.10-rc3-00004-gd073e0242f (Sep 20 2019 - 08:24:13 +0200)

CPU:   NXP i.MX8QM RevB A53 at 1200 MHz

Model: Advantech iMX8QM Qseven series
Board: ROM-7720-A1 4GB
Build: SCFW 65afe5f6
Boot:  SD2
DRAM:  4 GiB
MMC:   FSL_SDHC: 0, FSL_SDHC: 1, FSL_SDHC: 2
Loading Environment from MMC... OK
In:    serial@5a060000
Out:   serial@5a060000
Err:   serial@5a060000
Net:   eth0: ethernet@5b040000Could not get PHY for FEC1: addr 1
, eth-1: ethernet@5b050000
Hit any key to stop autoboot:  0

Signed-off-by: Oliver Graute <oliver.graute@kococonnector.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Ye Li <ye.li@nxp.com>
Cc: uboot-imx <uboot-imx@nxp.com>