helper: add bitfield helper macros

This patch ports FIELD_{GET,PREP,FIT} macros and related macro
from FreeBSD, referenced file:
- `src/tree/sys/compat/linuxkpi/common/include/linux/bitfield.h`

Checkpatch-ignore: MACRO_ARG_REUSE

Change-Id: I6fdf4514d3f95d62fadf7654409a4878d470a600
Signed-off-by: Walter Ji <walter.ji@oss.cipunited.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8171
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/helper/Makefile.am

@@ -19,6 +19,7 @@ noinst_LTLIBRARIES += %D%/libhelper.la
 	%D%/nvp.c \
 	%D%/align.h \
 	%D%/binarybuffer.h \
+	%D%/bitfield.h \
 	%D%/bits.h \
 	%D%/configuration.h \
 	%D%/list.h \