Remove FET mask debug code

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Reset PWM frequency to 31.25 kHz

We used 4 kHz temporarily to discover whether the high frequency damaged the
board.  We're now entering part 2/2 of that test.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Switch to using smaller integer types

Tested: Motors driven
Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>