tests: gen_isr_table: multilevel: cleanup filter & Kconfigs

The following Kconfigs are always enabled on `qemu_riscv32`:
- CONFIG_MULTI_LEVEL_INTERRUPTS
- CONFIG_2ND_LEVEL_INTERRUPTS
- CONFIG_RISCV_PRIVILEGED

No need to enable/filter for them in the testcase.

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