Add i2c_board_info for RiscPC PCF8583

Add the necessary i2c_board_info structure to fix the lack of PCF8583
RTC on RiscPC.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>