irq: multilevel: allow to APIs to always work

When `CONFIG_MULTI_LEVEL_INTERRUPTS` is enabled, bits in a
`uint32_t` is always partitioned into 3 levels, we can safely
remove the `CONFIG_*_LEVEL_INTERRUPTS` checks so that the
APIs always works.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>
Signed-off-by: Yong Cong Sin <yongcong.sin@gmail.com>