libpayload-x86: i8042: fix i8042_data_ready_ps2 and i8042_data_ready_aux

keyboard_disconnect was called without keyboard_init being called and in this
case keyboard_havechar returns true because i8042_data_ready_ps2 is
dereferencing uninitialized variable ps2_fifo from within fifo_is_empty causing
keyboard_disconnect to be stuck in this while loop.
while (keyboard_havechar())
    keyboard_getchar();

BUG=b:80299098
TEST=Check if the normal mode path in depthcharge is not causing a hang

Change-Id: I944b4836005c887a2715717dff2df1b5a220818e
Signed-off-by: Hannah Williams <hannah.williams@intel.com>
Reviewed-on: https://review.coreboot.org/26590
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

payloads/libpayload/drivers/i8042/keyboard.c

@@ -324,6 +324,9 @@ void keyboard_disconnect(void)
 	if (inb(0x64) == 0xFF)
 		return;
 
+	if (!i8042_has_ps2())
+		return;
+
 	/* Empty keyboard buffer */
 	while (keyboard_havechar())
 		keyboard_getchar();