rtc: Add Amlogic Virtual Wake RTC

rtc: Add Amlogic Virtual Wake RTC

The Amlogic Meson GX SoCs uses a special register to store the
time in seconds to wakeup after a system suspend.

In order to be able to reuse the RTC wakealarm feature, this
driver implements a fake RTC device which uses the system time
to deduce a suspend delay.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
[khilman: rebase to v5.3-rc, rework and modernization]
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20190812232850.8016-3-khilman@kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>