auxdisplay: provide hd44780_common_gotoxy

Provide a hd44780_common_gotoxy function and a pointer in the ops for
charlcd to use to move the cursor.

Reviewed-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Lars Poeschel <poeschel@lemonage.de>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>