libpayload: Bring keyboard_wait_write() back

Code is using it...

Change-Id: I6894b45cbbf70c8e7ce37ce18d93cadf0ea9fbfc
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/4649
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Nico Huber <nico.h@gmx.de>

payloads/libpayload/drivers/keyboard.c

@@ -258,6 +258,16 @@ int keyboard_getchar(void)
 	return ret;
 }
 
+static int keyboard_wait_write(void)
+{
+	int retries = 10000;
+
+	while(retries-- && (inb(0x64) & 0x02))
+		udelay(50);
+
+	return (retries <= 0) ? -1 : 0;
+}
+
 /**
  * Set keyboard layout
  * @param country string describing the keyboard layout language.