skge: remove broken and unused PHY_M_PC_MDI_XMODE macro

Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
Cc: Stephen Hemminger <shemminger@linux-foundation.org>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>