Move duplicated code to common/gdb_proc_service.h

This commit moves now-identical code from gdb/gdb_proc_service.h
and gdb/gdbserver/gdb_proc_service.h into the new shared file
gdb/common/gdb_proc_service.h.

gdb/ChangeLog:

	* common/gdb_proc_service.h: New file, factored out from...
	* gdb_proc_service.h: Moved common code to the above file.
	* Makefile.in (HFILES_NO_SRCDIR): Add the above new file.

gdb/gdbserver/ChangeLog:

	* gdb_proc_service.h: Moved common code to
	common/gdb_proc_service.h.