[ARM] Orion: enable CONFIG_RTC_DRV_M41T80 for D-Link DNS-323

The D-Link DNS-323 uses a M41T80 RTC chip, so enable this driver in
the Orion defconfig.

Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Cc: Herbert Valerio Riedel <hvr@gnu.org>
Acked-by: Nicolas Pitre <nico@marvell.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>