[ARM] 4732/1: GLAN Tank: register rtc-rs5c372 i2c device

Use the new i2c framework to load rtc-rs5c372 for the GLAN Tank.

Tested-by: Gordon Farquharson <gordonfarquharson@gmail.com>
Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Acked-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>