scripts/decodecode: set ARCH when running natively on arm/arm64

When running decodecode natively on arm64, ARCH is likely not to be set,
and we end-up with .4byte instead of .inst when generating the
disassembly.

Similar effects would occur if running natively on a 32bit ARM platform,
although that's even less popular.

A simple workaround is to populate ARCH when it is not set and that we're
running on an arm/arm64 system.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Marc Zyngier <[e-mail]>
Acked-by: Will Deacon <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

scripts/decodecode

···
 4) type=4byte ;;
 esac
 
+if [ -z "$ARCH" ]; then
+    case `uname -m` in
+	aarch64*) ARCH=arm64 ;;
+	arm*) ARCH=arm ;;
+    esac
+fi
+
 disas() {
 	${CROSS_COMPILE}as $AFLAGS -o $1.o $1.s > /dev/null 2>&1