Introduce and use new_breakpoint_from_type

Introduce and use new_breakpoint_from_type

This is a small preparatory patch to factor out a snippet that appears
twice.  More kinds of breakpoints will need to be created based on
bptype, so I think it's a good idea to centralize the instantiation of
breakpoint objects.

gdb/ChangeLog:

	* breakpoint.c (new_breakpoint_from_type): New function.
	(create_breakpoint_sal): Use new_breakpoint_from_type and
	unique_ptr.
	(create_breakpoint): Likewise.