scripts: xxdi.pl: add xxd -i compat mode

So it can serve as a standalone drop in replacement for xxd utility used
currently mostly in U-Boot packages with `xxd -i` mode which outputs C
include file style, with aim for byte to byte identical output, so the
eventual difference in the generated output is easily spottable.

Fixes: #10555
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: Jo-Philipp Wich <jo@mein.io> [perl-fu]

scripts/xxdi.pl

@@ -16,15 +16,21 @@ use strict;
 use warnings;
 
 my $indata;
+my $var_name = "stdin";
+my $full_output = (@ARGV > 0 && $ARGV[0] eq '-i') ? shift @ARGV : undef;
 
 {
 	local $/;
 	my $fh;
 
 	if (@ARGV) {
-		open($fh, '<:raw', $ARGV[0]) || die("Unable to open $ARGV[0]: $!\n");
-	} else {
+		$var_name = $ARGV[0];
+		open($fh, '<:raw', $var_name) || die("xxdi.pl: Unable to open $var_name: $!\n");
+	} elsif (! -t STDIN) {
 		$fh = \*STDIN;
+		undef $full_output;
+	} else {
+		die "usage: xxdi.pl [-i] [infile]\n";
 	}
 
 	$indata = readline $fh;
@@ -34,32 +40,27 @@ my $indata;
 
 my $len_data = length($indata);
 my $num_digits_per_line = 12;
-my $var_name;
-my $outdata;
+my $outdata = "";
 
 # Use the variable name of the file we read from, converting '/' and '.
 # to '_', or, if this is stdin, just use "stdin" as the name.
-if (@ARGV) {
-	$var_name = $ARGV[0];
-	$var_name =~ s/\//_/g;
-	$var_name =~ s/\./_/g;
-} else {
-	$var_name = "stdin";
-}
+$var_name =~ s/\//_/g;
+$var_name =~ s/\./_/g;
+$var_name = "__$var_name" if $var_name =~ /^\d/;
 
-$outdata .= "unsigned char $var_name\[] = {";
+$outdata = "unsigned char $var_name\[] = { " if $full_output;
 
-# trailing ',' is acceptable, so instead of duplicating the logic for
-# just the last character, live with the extra ','.
 for (my $key= 0; $key < $len_data; $key++) {
 	if ($key % $num_digits_per_line == 0) {
-		$outdata .= "\n\t";
+		$outdata = substr($outdata, 0, -1)."\n  ";
 	}
 	$outdata .= sprintf("0x%.2x, ", ord(substr($indata, $key, 1)));
 }
 
-$outdata .= "\n};\nunsigned int $var_name\_len = $len_data;\n";
+$outdata = substr($outdata, 0, -2);
+$outdata .= "\n";
 
-binmode STDOUT;
-print {*STDOUT} $outdata;
+$outdata .= "};\nunsigned int $var_name\_len = $len_data;\n" if $full_output;
 
+binmode STDOUT;
+print $outdata;