rt2x00: rt2800pci: split rt2800pci_enable_radio function

The function is called for PCI and SoC devices
however the MCU related part of the function
has no effect on SoC devices. Move the common
part of the function into a separate helper and
use that for the SoC devices.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>