net: dsa: microchip: Remove unused declarations

Commit 91a98917 ("net: dsa: microchip: move switch chip_id detection to ksz_common")
removed ksz8_switch_detect() but not its declaration.
Commit 6ec23aaa ("net: dsa: microchip: move ksz_dev_ops to ksz_common.c")
declared but never implemented other functions.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20230821125501.19624-1-yuehaibing@huawei.com


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