ARM: Orion5x: ts78xx: remove RTC detection

The rtc-m48t86 driver now handles the RTC detection. Remove the
redundant code from the platform.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-By: Alexander Clouter <alex+kernel@digriz.org.uk>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>