Provide an alternate implementation of Crit. Section for nRF5x

[rgrover]

We've explored the possibility of using target dependencies, but yotta doesn't allow us to say:

if Nordic:
  take nrf-atomic-ops
else if M0:
  take M0-atomic-ops
else:
  take generic-atomic-ops

@bogdanm @0xc0170 @bremoran @autopulated

[autopulated]

is there a #define that you can check that specifically tests for the presence of the softdevice?

[rgrover]

There is no #define to indicate a softdevice. The only other usable #define would be TARGET_NRF51822. We could introduce a macro USING_NRF_SOFTDEVICE if needed. is that a reasonable approach?

[autopulated]

In that case +1 as is.

[rgrover]

CR @bogdanm @0xc0170 @bremoran

[bremoran]

+1

[bogdanm]

Accepting this for now, we need to make it look better in the future.