drivers: misc: coresight: Add nrf_etr module

Add module which is dumping data from Coresight ETR buffer. Coresight
ETR is a sink for STMESP data. This module is specific to Nordic SoC
because it does not access ETR registers. Instead it is using Nordic
specific module (Trace Buffer Monitor TBM) to monitor amount of data
in the ETR buffer (which is a circular buffer).

Data from that buffer is sent over UART (in future it may be extended
to other transports). In future, module will be extended with option
to process STM data on chip.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>