boards: nxp: frdm_mcxn947: documentation fixes

Correct a few issues with the documentation that were causing rendering
issues, as well as the following changes:
- added blurb to debug section clarifying that the default debugger
  firmware supports LinkServer
- updated serial terminal output with board name given when building
  with HWMv2

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>