rt2x00: rt2800pci: rename rt2800pci_disable_radio function

The function contain code for SoC devices only.
Rename the function to 'rt2800soc_disable_radio'
and move it to the SoC specific section. Use
the renamed function in the SoC specific code
only and remove the 'if rt2x00_is_soc(rt2x00dev)'
condition from the function body.

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