net: dsa: qca8k: make mib autocast feature optional

Some switch may not support mib autocast feature and require the legacy
way of reading the regs directly.
Make the mib autocast feature optional and permit to declare support for
it using match_data struct in a dedicated qca8k_info_ops struct.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>