ARM: imx: Disable 1Gbps support on MCCMON6's KSZ9031 PHY

mccmon6 works in 10/100 MiB Ethernet environment, so disabling 1GiB support
improves robustness of the network after power up (as one don't need to
wait for autoneg).

Signed-off-by: Lukasz Majewski <lukma@denx.de>

include/configs/mccmon6.h

@@ -78,6 +78,7 @@
 	"fdt_high=0xffffffff\0" \
 	"initrd_high=0xffffffff\0" \
 	"boot_os=yes\0" \
+	"disable_giga=yes\0" \
 	"download_kernel=" \
 		"tftpboot ${kernel_addr} ${kernel_file};" \
 		"tftpboot ${fdt_addr} ${fdtfile};\0" \