scripts/checkstack.pl: Support huge stack sizes on arm64

arm64 uses this idiom to build huge stack frames:

    sub     sp, sp, #0x1, lsl Rust-for-Linux#12

Add support for this in checkstack.pl.

Signed-off-by: Asahi Lina <lina@asahilina.net>

scripts/checkstack.pl

@@ -57,7 +57,7 @@
 		#ffffffc0006325cc:       a9bb7bfd        stp     x29, x30, [sp, #-80]!
 		#a110:       d11643ff        sub     sp, sp, #0x590
 		$re = qr/^.*stp.*sp, \#-([0-9]{1,8})\]\!/o;
-		$dre = qr/^.*sub.*sp, sp, #(0x$x{1,8})/o;
+		$dre = qr/^.*sub.*sp, sp, #(0x$x{1,8})(?:, lsl #([0-9]*))?/o;
 	} elsif ($arch eq 'arm') {
 		#c0008ffc:	e24dd064	sub	sp, sp, #100	; 0x64
 		$re = qr/.*sub.*sp, sp, #([0-9]{1,4})/o;
@@ -183,8 +183,10 @@ sub arm_push_handling {
 	}
 	elsif (defined $dre && $line =~ m/$dre/) {
 		my $size = $1;
+		my $shift = $2;
 
 		$size = hex($size) if ($size =~ /^0x/);
+		$size = $size << $shift if $shift;
 		$total_size += $size;
 	}
 	elsif (defined $sub) {