INTERNAL: Change the compatible to distinguish qca8k platform

The compatible flag should be different for each board to match
with the dtb and to let coreboot pick the appropriate dtb.
The compatible is added to distinguish qca8k platform

Signed-off-by: Khasim Syed Mohammed <khasim.mohammed@linaro.org>
Change-Id: Idb46fee6fc87fed936479311e897f532d04c014f