drivers: ethernet: Fix device instance const qualifier loss

Passing driver's data to k_thread is sufficient for mcux.
On enc424j600, however, the device pointer is needed and thus is wrapped
into its data. But there seems to be a possible optimisation: all local
spi related function in fact only needs the device's data (context) and
so changing all spi related function to take the context would remove
the need to wrap the device pointer into its data.

Fixes #27399

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>