soc: riscv32: openisa_rv32m1: Fix build warnings
soc: riscv32: openisa_rv32m1: Fix build warnings

The INTMUX_LABEL define generated by DTS is marked as deprecated us
DT_OPENISA_RV32M1_INTMUX_INTMUX_LABEL instead.

Signed-off-by: Kumar Gala <a5e5248af4cd4f0ed8c515f61d40a6e2db46a66e@linaro.org>

ldts/zephyr,finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,ldts/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,Vudentz/zephyr,galak/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,galak/zephyr,GiulianoFranchetto/zephyr