Add device driver for a virtual RTC device in Android emulator.

The compatible string used by OS for binding the driver is defined
as "google,goldfish-rtc".
Signed-off-by: NMiodrag Dinic <miodrag.dinic@imgtec.com>
Signed-off-by: NGoran Ferenc <goran.ferenc@imgtec.com>
Signed-off-by: NAleksandar Markovic <aleksandar.markovic@imgtec.com>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>