arch: common: multilevel irq: move CAT_3RD_LVL_LIST into 3rd level guard

The `CAT_3RD_LVL_LIST` macro is only used when
`CONFIG_3RD_LEVEL_INTERRUPTS` is enabled, so move it into the
compiler guard.

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