helper: add bitmap helper primitives

Mainly copied/inspired from Linux kernel code in
- include/linux/types.h
- include/linux/bitmap.h
- include/linux/bitops.h

Change-Id: I317b542993ab81530c86553f339b79505d0fef0f
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/4894
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/helper/Makefile.am

@@ -16,6 +16,7 @@ noinst_LTLIBRARIES += %D%/libhelper.la
 	%D%/jep106.c \
 	%D%/jim-nvp.c \
 	%D%/binarybuffer.h \
+	%D%/bits.h \
 	%D%/configuration.h \
 	%D%/ioutil.h \
 	%D%/list.h \