libpayload/i8042: Add API to peek on keyboard input queue

Change-Id: I60699e044b5bacd3f5292fed7edbf529ae133284
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47592
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

payloads/libpayload/include/libpayload.h

@@ -233,6 +233,7 @@ u8 i8042_data_ready_ps2(void);
 u8 i8042_data_ready_aux(void);
 
 u8 i8042_read_data_ps2(void);
+u8 i8042_peek_data_ps2(void);
 u8 i8042_read_data_aux(void);
 
 int i8042_wait_read_ps2(void);