coreboot: Add peach pit chromebook configs

This adds coreboot configuration for the Samsung Chromebook 2 11", which
is based on the "google/peach_pit" mainboard in upstream coreboot. Also
adds a shared "peach" board directory to share with others having the
same baseboard.

The config is based on the following defconfig:

    CONFIG_VENDOR_GOOGLE=y
    CONFIG_CBFS_SIZE=0x00400000
    CONFIG_UART_FOR_CONSOLE=3
    CONFIG_BOARD_GOOGLE_PEACH_PIT=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 peach pit chromebook. This also fails
without a non-free 3rdparty/blobs/cpu/samsung/exynos5420/bl1.bin blob.

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

resources/coreboot/peach/board.cfg

+cbtree="peach"
+cbrevision="8da4bfe5b573f395057fbfb5a9d99b376e25c2a4" # 4.17
+romtype="normal"
+arch="ARMv7"
+payload_uboot="y"

resources/coreboot/peach_pit/board.cfg

+cbtree="peach"
+romtype="normal"
+arch="ARMv7"
+payload_uboot="y"