irqdomain: Use hwirq_max instead of revmap_size for NOMAP domains

NOMAP irq domains use the revmap_size field to indicate the maximum
hwirq number the domain accepts. This is a bit confusing as
revmap_size is usually used to indicate the size of the revmap array,
which a NOMAP domain doesn't have.

Instead, use the hwirq_max field which has the correct semantics, and
keep revmap_size to 0 for a NOMAP domain.

Signed-off-by: Xu Qiang <xuqiang36@huawei.com>
[maz: commit message]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220719063641.56541-3-xuqiang36@huawei.com