spi: spi_dw: Cleanup stale Kconfig symbols that should be DT
spi: spi_dw: Cleanup stale Kconfig symbols that should be DT

Instance 2 & 3 for some reason never transitioned CONFIG_SPI_*_IRQ_* to
DT prefix.  Fix that since those Kconfig symbols will never exist.

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

Vudentz/zephyr,ldts/zephyr,nashif/zephyr,explora26/zephyr,finikorg/zephyr,galak/zephyr,explora26/zephyr,galak/zephyr,explora26/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,ldts/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,ldts/zephyr,galak/zephyr,finikorg/zephyr,ldts/zephyr,Vudentz/zephyr,nashif/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,explora26/zephyr,explora26/zephyr