can: m_can: Move allocation of net device to probe

With the version no longer required to allocate the net device, it can
be moved to probe and the alloc_m_can_dev() function can be simplified.

Therefore, move the allocation of net device to probe and change
alloc_m_can_dev() to setup_m_can_dev().

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>