The 2011_1007_RT5390_RT5392_Linux_STA_V2.5.0.3_DPO
driver enables PCIe wakeup for these chips as well.
Do the same in rt2x00.

References:
  rt28xx_init in common/rtmp_init_intf.c
  RTMPInitPCIeLinkCtrlValue in os/linux/rt_rbus_pci_drv.c
Signed-off-by: NGabor Juhos <juhosg@openwrt.org>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>