scripts/decode_stacktrace.sh: add '-h' flag

When no parameters are passed, the usage instructions are presented only
when debuginfod-find is not found.  This makes sense because with
debuginfod none of the positional parameters are needed.  However it means
that users having debuginfod-find installed will have no chance of reading
the usage text without opening the file.

Many programs have a '-h' flag to get the usage, so add such a flag. 
Invoking 'scripts/decode_stacktrace.sh -h' will now show the usage text
and exit.

Link: https://lkml.kernel.org/r/20240823-decode_stacktrace-find_module-improvements-v2-3-d7a57d35558b@bootlin.comSigned-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Cc: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

scripts/decode_stacktrace.sh

@@ -7,6 +7,7 @@ usage() {
 	echo "Usage:"
 	echo "	$0 -r <release>"
 	echo "	$0 [<vmlinux> [<base_path>|auto [<modules_path>]]]"
+	echo "	$0 -h"
 }
 
 # Try to find a Rust demangler
@@ -33,7 +34,10 @@ READELF=${UTIL_PREFIX}readelf${UTIL_SUFFIX}
 ADDR2LINE=${UTIL_PREFIX}addr2line${UTIL_SUFFIX}
 NM=${UTIL_PREFIX}nm${UTIL_SUFFIX}
 
-if [[ $1 == "-r" ]] ; then
+if [[ $1 == "-h" ]] ; then
+	usage
+	exit 0
+elif [[ $1 == "-r" ]] ; then
 	vmlinux=""
 	basepath="auto"
 	modpath=""