amd-xgbe: Configuration and build support

This patch provides the Kconfig and Makefile changes needed
to configure and build the AMD 10GbE platform driver and the
AMD 10GbE phylib driver.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>