u-boot: Add veyron speedy chromebook configs

This adds U-Boot configuration for the ASUS Chromebook C201PA, also
known as "chromebook_speedy" in the U-Boot upstream defconfigs. Also
adds a shared "veyron" board directory to share with others having the
same 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 speedy chromebook.

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