x86: quark: Enable on-chip ethernet controllers

Intel Quark SoC integrates two 10/100 ethernet controllers which can
be connected to an external RMII PHY. The MAC IP is from Designware.
Enable this support with the existing U-Boot Designware MAC driver
so that the ethernet port on Intel Galileo board can be used.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>