soc: arm: arm: Select CPU DWT feature symbol for ARM Cortex-M SoCs

The Data Watchpoint and Trace (DWT) is an optional debug unit
for the Cortex-M family cores (except ARMv6-M; i.e. M0 and M0+)
that provides watchpoints, data tracing and system profiling
capabilities. We select it for the ARM Cortex-M SoCs
- Beetle
- Musca A, Musca B
since it is present in these SoCs.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>