libpayload: Add _ and + to USB HID keymap

Slightly more complete keymap

Change-Id: I4fef6b8f75ab07cb20a3a8ccd7eaad81c9fe719f
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/1922
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

payloads/libpayload/drivers/usb/usbhid.c

@@ -173,7 +173,7 @@ static const struct layout_maps keyboard_layouts[] = {
 	'U', 'V', 'W', 'X', 'Y', 'Z', '!', '@',
 	/* 0x20 */
 	'#', '$', '%', '^', '&', '*', '(', ')',
-	'\n', '\e', '\b', '\t', ' ', '-', '=', '[',
+	'\n', '\e', '\b', '\t', ' ', '_', '+', '[',
 	/* 0x30 */
 	']', '\\', -1, ':', '\'', '`', ',', '.',
 	'/', -1 /* CapsLk */, KEY_F(1), KEY_F(2), KEY_F(3), KEY_F(4), KEY_F(5), KEY_F(6),