rt2x00: rt2800pci: move SoC specific code into a separate module

The PCI and SoC specific drivers are using separate
code now so it is not reasonable to use the same
module for both drivers anymore.

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