arch: sw_isr: store device info in the table and add funtions to access

Change the internal function to `get_parent_entry`, which
returns the entire entry of table.

Store the parent interrupt controller device in the
`irq_parent_offset` table, and added 2 helper functions to:

1. determine the parent interrupt controller based on the IRQ
2. determine the IRQ of the parent interrupt controller

Declare the `struct _irq_parent_entry` in the header and added
`-` suffix to the struct so that it can be used to test the
functions in testsuites.

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