4.3.9.1 Cortex Trace support

Cortex trace may be enabled by setting CONFIG_CPU_ARM32M_TRACE. This is enough to enable related pins according to CONFIG_CPU_ARM32M_TRACE_PARALLEL.

User may tweak CONFIG_EFM32_TRACE_AUXHFCO_FREQ to a non-default value if needed. AUXHFRCO is clocking trace logic and cannot be disabled from clock driver for trace-enabled builds.