driver: interrupt_controller: nuclei_eclic: fixed interrupt level

CLIC should be the first level interrupt controller because it replaces
the basic RISC-V local interrupt.
The interrupt level in CLIC controls preemption between IRQs, rather than
specifying the number of nested interrupt controllers.
Removed CONFIG_MULTI_LEVEL_INTERRUPTS and the incorrect interrupt level.

Signed-off-by: Jimmy Zheng <jimmyzhe@andestech.com>