board/__init__: only declare max_num_displays when neeeded

Author: RetiredWizard

shared-module/board/__init__.c

@@ -176,7 +176,7 @@ mp_obj_t common_hal_board_create_uart(const mp_int_t instance) {
 #endif
 
 void reset_board_buses(void) {
-    #if CIRCUITPY_BOARD_I2C || CIRCUITPY_BOARD_SPI
+    #if CIRCUITPY_BOARD_I2C || (CIRCUITPY_BOARD_SPI && (CIRCUITPY_FOURWIRE || CIRCUITPY_SHARPDISPLAY || CIRCUITPY_AURORA_EPAPER))
     mp_int_t max_num_displays = CIRCUITPY_DISPLAY_LIMIT;
 
     #if CIRCUITPY_OS_GETENV