coccicheck: add M= option to control which dir is processed

Examples:
	make coccicheck M=drivers/net/wireless/
	make coccicheck SUBDIRS=drivers/net/wireless/

Version 2:
	fix patch file names when using M=
	tell coccinelle where the include files are

Version 3:
	Add second include option to support out of tree development
	Fix error message

Signed-off-by: Greg Dietsche <Gregory.Dietsche@cuw.edu>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Michal Marek <mmarek@suse.cz>