ARM: sa1100: remove unused RTC register definitions

Now that register definitions have been moved to the driver, we can remove
them from machine specific code.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>