Input: ams_delta_serio: Replace power GPIO with regulator

Modify the driver so it no longer requests and manipulates the
"keybrd_pwr" GPIO pin but a "vcc" regulator supply instead.

For this to work with Amstrad Delta, define a regulator over the
"keybrd_pwr" GPIO pin with the "vcc" supply for ams-delta-serio device
and register it from the board file.  Both assign an absulute GPIO
number to the soon depreciated .gpio member of the regulator config
structure, and also build and register a GPIO lookup table so it is
ready for use by the regulator driver as soon as its upcoming update
is applied.

Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>