uboot-imx

MA-14916-3: Add mx6/7 reference board support to enable android fastboot

this commit is based on the cherrypick of a patch from imx_v2018.03 with
below commit info:
"
commit f15e20eeb42d421d694e75d6f159d908b5606e1f
Author: Ye Li <ye.li@nxp.com>
Date:   Mon May 21 02:32:08 2018 -0700

MLK-18591-7 android: Add mx6/7 reference board support to enable android
fastboot

Add board level support for android fastboot feature. Each board has
a android specified header file for defining android related configuraitons.
And add build targets for their android uboot images building.
"
and then some modification is made to make the compilation pass.
the defconfig files modification is based on corresponding files from
BSP team, ucmd/acmd function is disabled for Android U-Boot.

with defconfig files for 6ul chips, the compilation will terminate with
failure on imx_v2018.03, so no modification was made on them.

Change-Id: Ibe5979239e5e6a78b06f332c9041d1f1de2566fc
Signed-off-by: Ye Li <ye.li@nxp.com>