bsp: nxp/mcx/mcxn/mcxn947: Remove invalid SPI8 entry.

Signed-off-by: Yilin Sun <imi415@imi.moe>

bsp/nxp/mcx/mcxn/frdm-mcxn947/board/Kconfig

@@ -81,10 +81,6 @@ menu "On-chip Peripheral Drivers"
                 config BSP_USING_SPI7
                     bool "Enable Flexcomm7 as SPI"
                     default n
-
-                config BSP_USING_SPI8
-                    bool "Enable Flexcomm8 as High Speed SPI"
-                    default y
             endif
 
     menuconfig BSP_USING_ADC