irqchip/imx-irqsteer: Support up to 960 input interrupts

The irqsteer IP routes groups of input interrupts to a dedicated system
interrupt per group. Each group handles 64 input interrupts.

The current driver is limited to 8 groups, i.e. 512 input interrupts, which
is sufficient for the existing i.MX SoCs. The upcoming i.MX94 family
extends the irqsteer IP to 15 groups, i.e. 960 interrupts.

Extending the group limit to 15 enables this, but the new SoCs are not
guaranteed to utilize all 15 groups. Unused groups have no mapping for the
underlying output interrupt, which makes the probe function fail as it
expects a valid mapping for each group output.

Remove this limitation and stop the mapping loop, when no valid mapping is
detected.

[ tglx: Massage change log ]

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/all/20250305095522.2177843-1-ping.bai@nxp.com