ARM: configs: at91: sama5: enable CAN PLATFORM driver

CAN_M_CAN_PLATFORM is needed to probe the driver on sama5 platforms
after the driver was split into multiple files.

Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>
Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200723162434.1983643-3-codrin.ciubotariu@microchip.com