dt-bindings: media: mediatek,jpeg: Relax IOMMU max item count

On MediaTek platforms with Multimedia MMU (M4U), a multimedia hardware
can be assigned with a local arbiter (LARB) which has a maximum of 32
ports for MediaTek's IOMMU infrastructure. That means there can be at
most 32 items in the iommus property in theory.

Instead of relaxing the max item count every time a newly introduced
device tree hits the limit, bump the number to 32 as an one-time effort.

On the other hand, all existing and foreseeable JPEG decoder nodes at
this point have at least 2 IOMMUs, so set minItems to 2 accordingly.

Signed-off-by: Fei Shao <fshao@chromium.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>