PiOS DSM: Use system clock to define time to run pulses at

There is a window after power is applied to send the binding pulses
to a satellite.  The hardcoded delay was board specific in terms of
working.  This uses the CPU clock to determine when to send the pulses
which should be reproducible.
Boards: remove commented PIOS_MASTER_CLOCK
F1: replace PIOS_MASTER_CLOCK with PIOS_SYSCLK

This makes F1 consistent with F3/4 implementations so
PIOS_SYSCLK can be assumed in common code.
Merge pull request #709 from peabody124/dsm_bind

PiOS DSM: Use system clock to define time to run pulses at