Staging: add Synaptics RMI4 touchpad driver support

Added the Synaptics RMI4 touchpad driver support.

Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Naveen Kumar Gaddipati <naveen.gaddipati@stericsson.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Christopher Heiny <cheiny@synaptics.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>