imx: imx7ulp: add EVK board support

Add EVK board support.
Add the evk dts file.

LOG:
U-Boot 2017.03-rc2-00038-gab86c1d (Feb 22 2017 - 15:59:58 +0800)

CPU:   Freescale i.MX7ULP rev1.0 at 500 MHz
Reset cause: POR
Boot mode: Dual boot
Model: NXP i.MX7ULP EVK
DRAM:  1 GiB
MMC:   FSL_SDHC: 0
In:    serial@402D0000
Out:   serial@402D0000
Err:   serial@402D0000
Net:   Net Initialization Skipped
No ethernet found.
Hit any key to stop autoboot:  0

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>