Add some guesses to FL2_copyIMG for older X200 extraction.

The FL2_copyIMG tool uses some heuristics to work out how to extract the
EC firmware image from inside the FL2 container.  Many of these are simply
guesses, so there are checks to try to only match files that "look" right.

Add some matches for the 7XHT21WW and 7XHT22WW firmware (See #104)

scripts/FL2_copyIMG

@@ -210,6 +210,7 @@ sub _check {
 
     # List of known file sizes (basically a doublecheck on the signature)
     my $known = {
+         4213270 => [0x290000, 0x20000],
          4240490 => [0x290000, 0x20000],
     };