imx: Add MYiR Tech MYS-6ULX support

MYS-6ULX is single board computer (SBC) comes with eMMC or NAND based
on imx6ULL SoC from NXP and provision for expansion board. This
commit adds support only for SBC with NAND.

CPU:   Freescale i.MX6ULL rev1.1 528 MHz (running at 396 MHz)
CPU:   Commercial temperature grade (0C to 95C) at 45C
Reset cause: WDOG
Model: MYiR i.MX6ULL MYS-6ULX Single Board Computer with NAND
Board: MYiR MYS-6ULX 6ULL Single Board Computer
DRAM:  256 MiB
NAND:  256 MiB
MMC:   FSL_SDHC: 0
In:    serial@2020000
Out:   serial@2020000
Err:   serial@2020000
Net:   FEC0

Working:
 - Eth0
 - MMC/SD
 - NAND
 - UART 1
 - USB host

Signed-off-by: Parthiban Nallathambi <parthiban@linumiz.com>