i2c: New Atmel AT91 bus driver

Add support for the I2C (Two-wire interface) controller integrated in
the Atmel AT91RM9200 processor.  This driver should also be usable on
the Atmel AT91SAM9261 and AT91SAM9260 processors.

Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>