net: dsa: ks8995: Delete sysfs register access

There is some sysfs file to read and write registers randomly
in the ks8995 driver.

The contemporary way to achieve the same thing is to implement
regmap abstractions, if needed. Delete this and implement
regmap later if we want to be able to inspect individual registers.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250813-ks8995-to-dsa-v1-3-75c359ede3a5@linaro.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>