MLK-12757-3: ARM: dts: imx6ull-ddr3-arm2-emmc.dts: add eMMC support

MLK-12757-3: ARM: dts: imx6ull-ddr3-arm2-emmc.dts: add eMMC support

For imx6ull-ddr3-arm2 board, eMMC and SD1 slot share usdhc1, so
this patch add another dts file imx6ull-ddr3-arm2-emmc.dts to
support eMMC.

eMMC data4~data7 share the same I/O domain with sd2, so this patch
only enable eMMC 4bit mode.

Due to the eMMC on imx6ull-ddr3-arm2 board support HS200 mode, and
need the VCCQ to be 1.8v, this patch keep usdhc vselect, let usdhc
to change the I/O voltage to 1.8v automatically. Otherwise, another
rework needed: remove R95, add R94.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>