spmi: mtk-pmif: Add multi-bus support for SPMI 2.0

spmi: mtk-pmif: Add multi-bus support for SPMI 2.0

In preparation for adding support for MT8196/MT6991 SoCs having
multiple SPMI busses, move the bus specific parameters into a new
pmif_bus structure and keep the SoC-specific data in the already
existing struct pmif, and add means to register multiple SPMI
controllers.

While this needs a different devicetree node structure, where each
of the controllers are in subnodes of a main SPMI node, and where
each has its own resources (iospaces and clocks), support for the
legacy single-controller was retained and doesn't require any DT
change in the currently supported SoCs.

Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Link: https://patch.msgid.link/20260123182039.224314-3-sboyd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>