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
Cc: Stefano Babic
Cc: Fabio Estevam
Cc: Peng Fan
Cc: Simon Glass
Cc: Ye Li
Cc: uboot-imx