helper: Add generic little endian CRC32 function

This generalizes the little endian CRC32 function used in the OR1K
target and moves it to a common helper, so that other places do not need
to reinvent the wheel. It is directly used in the OR1K target.

Change-Id: I0e55340281a5bfd80669bb1994f3a96fecc1248a
Signed-off-by: Marian Buschsieweke <marian.buschsieweke@ovgu.de>
Reviewed-on: https://review.openocd.org/c/openocd/+/7415
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/helper/Makefile.am

@@ -9,6 +9,7 @@ noinst_LTLIBRARIES += %D%/libhelper.la
 	%D%/configuration.c \
 	%D%/log.c \
 	%D%/command.c \
+	%D%/crc32.c \
 	%D%/time_support.c \
 	%D%/replacements.c \
 	%D%/fileio.c \
@@ -24,6 +25,7 @@ noinst_LTLIBRARIES += %D%/libhelper.la
 	%D%/types.h \
 	%D%/log.h \
 	%D%/command.h \
+	%D%/crc32.h \
 	%D%/time_support.h \
 	%D%/replacements.h \
 	%D%/fileio.h \