ralink: fix pcie reset

some old mt7620a uboots dont reset the pcie core properly. work around this
issue in the kernel driver.

Signed-off-by: John Crispin <blogic@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43292 3c298f89-4303-0410-b956-a3cf2f4a3e73