reset: Add Raspberry Pi 4 firmware reset controller

reset: Add Raspberry Pi 4 firmware reset controller

Raspberry Pi 4's co-processor controls some of the board's HW
initialization process, but it's up to Linux to trigger it when
relevant. Introduce a reset controller capable of interfacing with
RPi4's co-processor that models these firmware initialization routines as
reset lines.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Link: https://lore.kernel.org/r/20200629161845.6021-3-nsaenzjulienne@suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>