i2c-sibyte: SWARM I2C board initialization

 The standard rtc-m41t80.c driver cannot be used with the SWARM as it is,
because the board does not provide setup information for the I2C core.  
As a result the bus and the address to probe for the M41T80 chip is not
known.

 Here is a set of changes that fix the problem:

1. swarm-i2c.c -- SWARM I2C board setup, currently for the M41T80 chip on 
   the bus #1 only (there is a MAX6654 temperature sensor on the bus #0 
   which may be added in the future if we have a driver for that chip).

2. The i2c-sibyte.c BCM1250A SMBus controller driver now registers its 
   buses as numbered so that board setup is correctly applied.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Jean Delvare <khali@linux-fr.org>