can: tcan4x5x: rename tcan4x5x.c -> tcan4x5x-core.c

This is a preparation patch to move the regmap related code into a seperate
file. This patch removes the tcan4x5x.c to tcan4x5x-core.c.

Reviewed-by: Dan Murphy <dmurphy@ti.com>
Tested-by: Sean Nyekjaer <sean@geanix.com>
Link: https://lore.kernel.org/r/20201215231746.1132907-4-mkl@pengutronix.de


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>