rtl8180: add RF code for rtl8225 zebra v4

This patch introduce new RF code for rtl8225 zebra v4 radio
frontend.

This code contains a lot of black magic and it can work probably
only with the radio embdedded in the rtl8187se single-chip.

Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>