staging: pi433: Combine all rf69_set_amplifier_x()

Replaces the functions rf69_set_amplifier_1, _2, _3 with two
functions: rf69_enable_amplifier(dev, amp_mask) and
rf69_disable_amplifier(dev, amp_mask).

Signed-off-by: Simon Sandström <simon@nikanor.nu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>