Add devicetree for Gumstix Pepper SBC

Signed-off-by: Ash Charles <ashcharles@gmail.com>
[HACK] Invert the y-axis of the touchscreen for pepper

Signed-off-by: Ash Charles <ashcharles@gmail.com>
Add a defconfig for pepper

Signed-off-by: Ash Charles <ashcharles@gmail.com>