serial: correct documentation regarding hold/reset

The warning about GPIO configuration was misleading in its description
and was misplaced.
reindent: using astyle 2.04

Visible changes:
- Pointer-to-pointer no longer has internal whitespace ("* *" -> "**")
- Some attached brackets were separated
- Comments in switch statements now align with case.  This is undesired
  because /*FALLTHRU*/ now shifts rather than being aligned with the
  code that falls through, but conceptually it could just as well bind
  with the case statement so we'll accept it.
u8g: accommodate upstream API change