sunxi: add MACPWR in Orange Pi PC2 defconfig

The Ethernet function is enabled in the Orange Pi PC2 device tree and
defconfig, however, CONFIG_MACPWR is not properly set, which left the
PHY being disabled when booting, which makes the Ethernet function not
usable.

Add the proper value of this option in the PC2 defconfig.

Fixes: e7bd15ea ("sunxi: Add OrangePi PC 2 initial support")
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>