spmi: mtk-pmif: Implement Request Capable Slave (RCS) interrupt

spmi: mtk-pmif: Implement Request Capable Slave (RCS) interrupt

Add support for the per-bus RCS interrupt by adding a new linear
irqdomain and its irqchip.

The SPMI controller will raise an interrupt when any of the SPMI
connected devices' irq needs attention (whenever any interrupt
fires on any SID) in one of four registers, where each register
holds four sets of four bits of information about a SID interrupt.

This controller's RCS interrupt status knowledge is limited to the
address of the SID that raised an interrupt, but does not have any
details about the devices irq numbers: as this may change with a
future SPMI controller IP version, the devicetree is meant to hold
three cells, where the first one is the SPMI SID interrupt number,
the second one is a device interrupt number, and the third one is
the irq sense type.

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/20260123182039.224314-5-sboyd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>