rt2x00: rt2800pci: use separate hwcrypt_disabled callback for SoC devices

The 'rt2800pci_hwcrypt_disabled' function is the
only PCI specific callback which is used by the
SoC driver. Create a clone of that to get rid of
the dependency.

Even though the two functions are using the same
variable, but the SoC specific code will be moved
into a separate module which will have its own
'modparam_nohwcrypt' variable.

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