irqchip/gic-v3-its: Limit number of per-device MSIs to the range the ITS supports

irqchip/gic-v3-its: Limit number of per-device MSIs to the range the ITS supports

The ITS driver blindly assumes that EventIDs are in abundant supply, to the
point where it never checks how many the hardware actually supports.

It turns out that some pretty esoteric integrations make it so that only a
few bits are available, all the way down to a single bit.

Enforce the advertised limitation at the point of allocating the device
structure, and hope that the endpoint driver can deal with such limitation.

Fixes: 84a6a2e7fc18d ("irqchip: GICv3: ITS: device allocation and configuration")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Zenghui Yu <zenghui.yu@linux.dev>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260206154816.3582887-1-maz@kernel.org