[ARM] Acorn: move the i2c bus driver into drivers/i2c

Move the Acorn IOC/IOMD I2C bus driver from drivers/i2c, strip
out the reminants of the platform specific parts of the old
PCF8583 RTC code, and remove the old obsolete PCF8583 driver.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>