rtc: m48t86: move m48t86.h to platform_data

m48t86.h belongs to include/linux/platform_data/

Acked-by: Jason Cooper <jason@lakedaemon.net>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Alexander Clouter <alex@digriz.org.uk>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>