Use ifdefs to remove more code around RC option code

[peterbarker]

Moves us closer to being able to remove default: clauses.

Board               AP_Periph  blimp  bootloader  copter  heli  iofirmware  plane  rover  sub
Durandal                       *      *           *       *                 *      *      *
KakuteH7-bdshot                *      *           *       *                 *      *      *
MatekF405                      -16    *           -56     -48               -40    -16    -8
Pixhawk1-1M-bdshot             -16                -16     -16               -16    -16    -16
f303-Universal      *
iomcu                                                           *
revo-mini                      -8     *           -8      -8                -16    -8     -16

real    5m21.096s
user    133m52.460s
sys     18m32.352s

[tridge]

@peterbarker please test code size on AP_Periph targets too before merge, thanks!

[rmackay9]

Thanks for the Topotek fix!