[bios] Use INT 16,11 instead of INT 16,01 to check for keystrokes

INT 16,01 will discard some extended keystrokes on some BIOSes, making
it impossible for iPXE to detect keypresses such as F12.  Fix by using
INT 16,11 instead.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/firmware/pcbios/bios_console.c

@@ -286,7 +286,7 @@ static int bios_iskey ( void ) {
 					   "popw %w0\n\t"
 					   "cli\n\t" )
 			       : "=r" ( flags ), "=a" ( discard_a )
-			       : "a" ( 0x0100 ) );
+			       : "a" ( 0x1100 ) );
 	return ( ! ( flags & ZF ) );
 }