can: m_can: add CONFIG_HAS_IOMEM dependence

m_can uses io memory which makes it not compilable on architectures
without HAS_IOMEM such as UML:

drivers/built-in.o: In function `m_can_plat_probe':
m_can.c:(.text+0x218cc5): undefined reference to `devm_ioremap_resource'
m_can.c:(.text+0x218df9): undefined reference to `devm_ioremap'

Signed-off-by: David Cohen <david.a.cohen@linux.intel.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>