ARM: dts: Add minimal support for motorola droid 4 xt894

Let's add minimal support for droid 4 with MMC and WLAN working.
It can be booted with appended dtb using kexec to a state where
MMC and WLAN work with currently no support for it's PMIC or
display.

Note that we are currently using fixed regulators as we don't
have support for it's cpcap PMIC. I'll be posting regmap_spi
based minimal cpcap patches later on for USB and the debug
UART on droid 4 multiplexed with the USB connector.

Cc: Marcel Partap <mpartap@gmx.net>
Cc: Michael Scott <michael.scott@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>