driver: interrupt_controller: Filter invalid channel for RV32M1 SOC

Invalid channel should be filtered in intmux isr, please refer to
page 1243~1244 of chapter 36 INTMUX of RV32M1 RM.

Note: Unlike the NVIC, the INTMUX does not latch pending source
interrupts. This means that the INTMUX output channel ISRs must
check for and handle a 0 value of the CHn_VEC register to account
for spurious interrupts.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>