Currently, the Goldfish RTC driver exclusively relies on device tree
to retrieve the base address, failing immediately if dev_read_addr()
returns FDT_ADDR_T_NONE. This restriction prevents the driver from
being used on platforms that instantiate devices via U_BOOT_DRVINFO()
instead of device tree, such as the QEMU m68k virt machine.

Add support for platform data to address this limitation. Introduce a
new .of_to_plat hook to handle device tree parsing and populate the
platform data. Update the probe function to rely exclusively on this
platform data, enabling support for both Device Tree and manual
instantiation.

Introduce a new header file include/goldfish_rtc.h to define the
platform data structure.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

Replace the incorrect description that was copied from another driver.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

There is no need to export goldfish_rtc_probe().

Fixes: 2d6dc19fd25d ("rtc: driver for Goldfish RTC")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

The Goldfish RTC is a virtual device which may be supplied by QEMU.
It is enabled by default on QEMU's RISC-V virt machine.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>