net: dsa: qca8k: initial conversion to regmap helper

Convert any qca8k set/clear/pool to regmap helper and add
missing config to regmap_config struct.
Read/write/rmw operation are reworked to use the regmap helper
internally to keep the delta of this patch low. These additional
function will then be dropped when the code split will be proposed.

Ipq40xx SoC have the internal switch based on the qca8k regmap but use
mmio for read/write/rmw operation instead of mdio.
In preparation for the support of this internal switch, convert the
driver to regmap API to later split the driver to common and specific
code. The overhead introduced by the use of regamp API is marginal as the
internal mdio will bypass it by using its direct access and regmap will be
used only by configuration functions or fdb access.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>