Input: goodix - add a goodix.h header file

Input: goodix - add a goodix.h header file

Add a goodix.h header file, and move the register definitions,
and struct declarations there and add prototypes for various
helper functions.

This is a preparation patch for adding support for controllers
without flash, which need to have their firmware uploaded and
need some other special handling too.

Since MAINTAINERS needs updating because of this change anyways,
also add myself as co-maintainer.

Reviewed-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20210920150643.155872-3-hdegoede@redhat.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>