Remove the hard-coded assumption that the EC is always 128K, as ITE
chips can also be 256K (which Clevo has started using since addw4).
Instead assume the ROM is correctly sized, which we do since
0d83819a21
("Pad binary file to total flash size") and proprietary
firmware has always done.
Signed-off-by: Tim Crawford <tcrawford@system76.com>