Add comments about using segments instead of sections.

This commits marks the end of this work on using sections to set the address
space of a type.  After discussing this at the GNU Cauldron, we should be
looking at the segments instead.

2014-07-29  Pierre Langlois  <pierre.langlois@embecosm.com>

	* gdbarch.h: Regenerate.
	* gdbarch.sh (symbol_type_from_section): Add a comment about using
	segments instead of sections.
	* avr-tdep.c (avr_symbol_type_from_section): Likewise.