coreboot: Add veyron speedy chromebook configs

This adds coreboot configuration for the ASUS Chromebook C201PA, which
is based on the "google/veyron" mainboard in upstream coreboot. Also
adds a shared "veyron" board directory to share with others having the
same baseboard.

The config is based on the following defconfig:

    # CONFIG_USE_BLOBS is not set
    CONFIG_VENDOR_GOOGLE=y
    CONFIG_CBFS_SIZE=0x400000
    CONFIG_BOARD_GOOGLE_VEYRON_SPEEDY=y
    CONFIG_CONSOLE_CBMEM_BUFFER_SIZE=0x20000
    CONFIG_UART_PCI_ADDR=0x0
    CONFIG_I2C_TRANSFER_TIMEOUT_US=500000

Untested since I don't have the veyron speedy chromebook.

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