board: toradex: Add Verdin iMX8M Mini support

This adds initial minimal support for the Toradex Verdin iMX8M Mini Quad
2GB WB IT V1.0A module. They are now strapped to boot from eFuses which
are factory fused to properly boot from their on-module eMMC. U-Boot
supports booting from the on-module eMMC only, SDP support is disabled
for now due to missing i.MX 8M Mini USB support.

Functionality wise the following is known to be working:
- eMMC, 8-bit and 4-bit MMC/SD card slots
- Ethernet
- GPIOs
- I2C

Boot sequence is:
SPL ---> ATF (TF-A) ---> U-boot proper

ATF, U-boot proper and u-boot.dtb images are packed into a FIT image,
loaded by SPL.

Boot:
U-Boot SPL 2020.01-00187-gd411d164e5 (Jan 26 2020 - 04:47:26 +0100)
Normal Boot
Trying to boot from MMC1
NOTICE:  Configuring TZASC380
NOTICE:  RDC off
NOTICE:  BL31: v2.0(release):rel_imx_4.14.98_2.3.0-0-g09c5cc994-dirty
NOTICE:  BL31: Built : 01:11:41, Jan 25 2020
NOTICE:  sip svc init

U-Boot 2020.01-00187-gd411d164e5 (Jan 26 2020 - 04:47:26 +0100)

CPU:   Freescale i.MX8MMQ rev1.0 at 0 MHz
Reset cause: POR
DRAM:  2 GiB
MMC:   FSL_SDHC: 0, FSL_SDHC: 1, FSL_SDHC: 2
Loading Environment from MMC... OK
In:    serial
Out:   serial
Err:   serial
Model: Toradex Verdin iMX8M Mini Quad 2GB Wi-Fi / BT IT V1.0A, Serial#
 06535149
Net:   eth0: ethernet@30be0000
Hit any key to stop autoboot:  0
Verdin iMX8MM #

Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>