can: mcp251xfd: rename driver files and subdir to mcp251xfd

In [1] Geert noted that the autodetect compatible for the mcp25xxfd driver,
which is "microchip,mcp25xxfd" might be too generic and overlap with upcoming,
but incompatible chips.

In the previous patch the autodetect DT compatbile has been renamed to
"microchip,mcp251xfd", this patch changes the name of the driver subdir and the
individual files accordinly.

[1] http://lore.kernel.org/r/CAMuHMdVkwGjr6dJuMyhQNqFoJqbh6Ec5V2b5LenCshwpM2SDsQ@mail.gmail.com

Link: https://lore.kernel.org/r/20200930091424.792165-8-mkl@pengutronix.de


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
(cherry picked from commit 1f0e21a0)
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>