gdb: add all_bp_locations function

gdb: add all_bp_locations function

Add the all_bp_locations function to replace the ALL_BP_LOCATIONS macro.
For simplicity, all_bp_locations simply returns a const reference to the
bp_locations vector.  But the callers just treat it as a range to
iterate on, so if we ever change the breakpoint location storage, we can
change the all_bp_locations function to return some other range type,
and the callers won't need to be changed.

gdb/ChangeLog:

	* breakpoint.c (ALL_BP_LOCATIONS): Remove, update users to use
	all_bp_locations.
	(all_bp_locations): New.

Change-Id: Iae71a1ba135c1a5bcdb4658bf3cf9793f0e9f81c