Issue #384 : support all board channel banks update rates in GCS

Each boards maps output channels by banks (up to 6) for update rate settings.
GCS used hardcoded values in the config widget, all board-specific values are
now moved to board plugins, and the config gadget queries the board for the
mappings.

Please confirm mapping for Sparky is correct.
sim sensors: avoid divide by zero in magOffsetEstimation
gdb: add config config files for missing targets
watchdog: clear wdg backup register during init

Using the PIOS_WDG_REGISTER slot in the backup registers is
a useful debug tool but it is important to ensure that this
state cannot influence the watchdog behaviour on future reboots.

Specifically, if a future boot removes one of the modules that
was previously watched by the watchdog, we don't want that
removal to endlessly trigger a watchdog.

F1 variant was actually clearing the flag, but was actually
doing it *before* caching the value for debug purposes.  F3/F4
variants were carrying state across a reboot which is bad for
the reasons listed above.
Merge pull request #724 from solidgoldbomb/sim-fix-nan-attitude

sim sensors: avoid divide by zero in magOffsetEstimation
sim-posix: align some sim copies of drivers to match real drivers
sim-posix: use real pios drivers whenever possible instead of copying
sim-posix: remove all unnecessary copies of pios drivers
sim-osx: remove all unnecessary copies of pios drivers
sim: align osx and posix sim driver variants wherever possible
sim-posix: misc makefile cleanup
sim-osx: use real pios drivers whenever possible instead of copying
sim makefiles: align makefiles between osx and posix sims
sim: provide missing definition of pios_com_debug_id
sim: provide weakly linked versions of external sim
pios tim: uint32_t -> uintptr_t
pios rtc: uint32_t -> uintptr_t
pios com: uint32_t -> uintptr_t

This change makes the code work for 64-bit compilations
as well as 32-bit (i.e. sim).

The lower drivers will be updated in separate commits
pios tcp/udp: uint32_t -> uintptr_t
pios usart: uint32_t -> uintptr_t