dwc2: fix efm32 host build and build efm32 in CI (#4090)

dwc2_efm32.h lacked dwc2_int_set(), which hcd_dwc2.c calls, so host/audio_host failed to build for sltb009a; the efm32 USB IRQ now dispatches by role via tusb_int_handler(). CI never built efm32: add it to the matrix and fetch CMSIS_5 for it.

Fixes #4082