u-boot: Add bob chromebook configs

This adds U-Boot configuration for the ASUS Chromebook Flip C101,
also known as "chromebook_bob" in the U-Boot upstream defconfigs. It
uses the shared tree for the "gru" baseboard.

The config has the following diffconfig from kevin:

    # chromebook_bob instead of chromebook_kevin
     DEFAULT_DEVICE_TREE "rk3399-gru-kevin" -> "rk3399-gru-bob"
     DEFAULT_FDT_FILE "rockchip/rk3399-gru-kevin.dtb" -> "rockchip/rk3399-gru-bob.dtb"
     OF_LIST "rk3399-gru-kevin" -> "rk3399-gru-bob"
     SPL_OF_LIST "rk3399-gru-kevin" -> "rk3399-gru-bob"
     TARGET_CHROMEBOOK_BOB n -> y
     TARGET_CHROMEBOOK_KEVIN y -> n

    # Display resolution is 1280x800, and no need for the big font
     VIDEO_FONT_8X16 n -> y
     VIDEO_FONT_TER16X32 y -> n
     VIDEO_ROCKCHIP_MAX_XRES 2400 -> 1280
     VIDEO_ROCKCHIP_MAX_YRES 1600 -> 800

Untested since I don't have the bob chromebook.

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

resources/u-boot/gru_bob/board.cfg

+ubtree="gru"
+arch="AArch64"