net: gem: Move gem to Kconfig

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>
diff --git a/configs/zynq_zc770_xm012_defconfig b/configs/zynq_zc770_xm012_defconfig
index a8f28da..4e963a4 100644
--- a/configs/zynq_zc770_xm012_defconfig
+++ b/configs/zynq_zc770_xm012_defconfig
@@ -11,3 +11,4 @@
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_PHYLIB=y
+CONFIG_ZYNQ_GEM=y