flashmax.pl: fix --esponly, clean up some error messages

Actually implement --esponly. Clean up some unnecessary error
messages.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

tools/flashmax.pl

@@ -150,8 +150,6 @@ my $esptool;
 
 # Try running esptool --help and look for a version string
 sub try_esptool($) {
-    use Data::Dump 'pp';
-
     my($cmd) = @_;
 
     return undef if ($cmd eq '');
@@ -592,7 +590,7 @@ sub upload_fpgadata($$) {
 	require Win32::SerialPort;
 	Win32::SerialPort->import(qw(:STAT));
 	'Win32::SerialPort';
-    } || die "$0: need Device::SerialPort or Win32::SerialPort\n";
+    } || die "$0: need Device::SerialPort (Unix/MacOS) or Win32::SerialPort (Win32)\n";
 
     print STDERR "Waiting for reinit...\n";
     usleep(4000000);
@@ -904,7 +902,7 @@ if (scalar(@espfiles)) {
 		'-z', map { (sprintf('0x%x', $_->[0]), $_->[1]) } @espfiles);
 }
 
-if (defined($fpgadata)) {
+if (!$esponly && defined($fpgadata)) {
     upload_fpgadata($port, $fpgadata);
 }