soc/soc.mk: Make rules for SoC
soc/soc.mk: Make rules for SoC

Copied rules from Makefile in root directory into specific makefile in
the SoC directory.

In future, the Makefile in the root directory will be removed.

Signed-off-by: Alan Green <97e77871b5fcc4941bebceb4338c97c1fd149f8c@google.com>

google/CFU-Playground,google/CFU-Playground,google/CFU-Playground,google/CFU-Playground