scripts/checkstack.pl: Fix arm64 wrong or unknown architecture

The following error occurs for the `make ARCH=arm64 checkstack` case:

aarch64-linux-gnu-objdump -d vmlinux $(find . -name '*.ko') | \
perl ./scripts/checkstack.pl arm64
wrong or unknown architecture "arm64"

As suggested by Masahiro Yamada, fix the above error using regular
expressions in the same way it was fixed for the `ARCH=x86` case via
commit fda9f990 ("scripts/checkstack.pl: automatically handle
32-bit and 64-bit mode for ARCH=x86").
Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: George G. Davis <george_davis@mentor.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/checkstack.pl

@@ -46,7 +46,7 @@ my (@stack, $re, $dre, $x, $xs, $funcre);
 	$x	= "[0-9a-f]";	# hex character
 	$xs	= "[0-9a-f ]";	# hex character or space
 	$funcre = qr/^$x* <(.*)>:$/;
-	if ($arch eq 'aarch64') {
+	if ($arch =~ '^(aarch|arm)64$') {
 		#ffffffc0006325cc:       a9bb7bfd        stp     x29, x30, [sp, #-80]!
 		#a110:       d11643ff        sub     sp, sp, #0x590
 		$re = qr/^.*stp.*sp, \#-([0-9]{1,8})\]\!/o;