rtc: goldfish: remove dependency to OF

We want to use the goldfish RTC on a machine without OF.
As there is no real dependency on it, remove the OF dependency from the
goldfish entry in Kconfig

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210323221430.3735147-2-laurent@vivier.eu