auxdisplay: add home to charlcd_ops

This adds a home function to the charlcd_ops struct and offer an
implementation for hd44780_common. This implementation is used by our
two hd44780 drivers. This is to make charlcd device independent.

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