INTERNAL: Change the compatible to distinguish platforms

The compatible flag should be different for each board to match
with the dtb and to let coreboot pick the appropriate dtb.
Hence this change.

Signed-off-by: Khasim Syed Mohammed <khasim.mohammed@linaro.org>
Change-Id: Iad780a8b3b98a4198fa28741ddfd6ce28d669c2b