rt2x00: convert RT2800PCI_PCI and RT2800PCI_SOC Kconfig symbols to booleans.

There is no need for Kconfig symbols RT2800PCI_PCI and RT2800PCI_SOC to be
tristates, as they are only used to check whether RT2800 PCI or SOC support
is to be compiled in.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>