mac80211: add rt2x00-mmio package to store the common parts for SoC and PCI access

This should fix a build error on ramips.


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36978 3c298f89-4303-0410-b956-a3cf2f4a3e73
Basic changes for AsiaRF module