Add support for RTC in M2M: Firmware

[sy2002]

As soon as we support the RTC in hardware (https://github.com/sy2002/MiSTer2MEGA65/issues/29) then we can start tackling it in the firmware.

One obvious idea what the firmware can do with an RTC is:

Files on the SD card (FAT32) that are written to/changed, for example disk images, can showing the updated date/time in future.

Maybe there are even more ideas.

The firmware part is not a low hanging fruit for the R4/R5 surge.