Revert "cubietruck: use GMAC instead of EMAC"

This reverts commit 5f760dd96bf5929a198da939e6c2e70ba19cf074.

fixed with commit e3fe51a37a4520868b3f61a1c3bf9916776b7315 and d498e0c5ca6f910f4ecf5237cffb9811adf08587