rtc: goldfish: Remove GOLDFISH dependency

Goldfish platform is covered with dust.
However the goldfish-rtc had been used as virtualized RTC
in QEMU for RISC-V virt hw and MIPS loongson3-virt hw, thus
we can drop other parts of goldfish but leave goldfish-rtc here.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20201114130921.651882-2-jiaxun.yang@flygoat.com