tests: kernel: gen_isr_table: rework multi_level_bit_masks tests

Reworked and combined the multi-level interrupt bit masks tests
to work on any configuration of bits in every level.

Updated the bits configuration in the testcase to use
non-symetric numbers so that shifting a level with the wrong
number of bits will certainly cause the test to fail.

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