Add PCF8563 RTC support to the Pi Build

A number of useful add-ons for the Pi include an RTC, some use an PCF8563 which is currently not supported by RISC OS. Anyone up for the challenge of adding it?

In the short term we might write a BASIC utility to read and set the RTC but updating the Pi ROM is what is really needed but that is beyond our area of expertise.

It uses a different I2C address and slightly different data format to the PCF8583 RTC which is supported in the RiscPC ROM.

http://www.nxp.com/docs/en/data-sheet/PCF8563.pdf
http://www.nxp.com/docs/en/data-sheet/PCF8583.pdf

IIC address:
8583: read=&A1, write=&A0
8563: read=&A3, write=&A2