u-boot: Add veyron mickey chromebit configs

This adds U-Boot configuration for the ASUS Chromebit CS10, also known
as "chromebit_mickey" in the U-Boot upstream defconfigs. It uses the
shared tree for the "veyron" baseboard. The config is almost the same as
upstream defconfig, but with REMAKE_ELF and POSITION_INDEPENDENT
enabled.

Untested since I don't have the veyron mickey chromebit.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>

resources/u-boot/veyron_mickey/board.cfg

+ubtree="veyron"
+arch="ARMv7"