[nrf52][tick] improve RTC use for LK tick
[nrf52][tick] improve RTC use for LK tick

Using the RTC1 module for the LK tick (instead of arm systick)
Use the nrf_hal library for peripheral manipulation instead of
direct register access.  Fixed race condition in current_time_hires
which would result in non monotonic readings.

Tested with clock_tests on:
  nrf52-pca10040-test  (nrf52832)
  nrf52-pca10056-test  (nrf52840)

littlekernel/lk,hollanderic/lkstuff,hollanderic/lkstuff,littlekernel/lk,hollanderic/lkstuff,hollanderic/lkstuff,littlekernel/lk,littlekernel/lk