sw_isr_table: Force align _isr_list_sname instances

For some target and optimization level combinations (aarch64 and -O2, for
example), GCC will over align _isr_list_sname instances. The local isr
declaration parser doesn't expect the extra padding that may be introduced
and will produce unexpected errors about bad IRQs (`error: IRQ 1903323438
(offset=0) exceeds the maximum of 42`, for example). Prevent this issue by
forcing the expected alignment of _isr_list_sname.

Fixes #81254

Signed-off-by: Jonathon Penix <jpenix@quicinc.com>