New opcode for 32->64 bit sign-extended immediate with warning

Add a new opcode for 32->64 bit sign-extended immediate, with warning
on the number not matching.

This unfortunately calls for an audit of all the \4[0123] opcodes, if
they should be replaced by \25[4567].  This only replaces one
instruction (MOV reg64,imm32); other instructions need to be
considered.

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

disasm.c

@@ -513,6 +513,7 @@ static int matches(const struct itemplate *t, uint8_t *data,
 	    break;
 
 	case4(040):
+	case4(0254):
             opx->offset = getu32(data);
 	    data += 4;
 	    break;