rtl8180: introduce functions for setting ANAPARAM 2 and 3 params

rtl8180 has one register for analog converters setting ,rtl8185 has
two and rtl8187se has three.
Setting those registers require more than a simple write, and for
one of them a function is already provided.
This patch introduces functions for the other two.
rtl8187se will use them. rtl8185 doesen't yet, but should

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