AP_BoardConfig: default to 6 PWM on FMUv4

less likely to use relays

libraries/AP_BoardConfig/AP_BoardConfig.cpp

@@ -33,7 +33,10 @@
 #ifdef CONFIG_ARCH_BOARD_PX4FMU_V1
 #define BOARD_PWM_COUNT_DEFAULT 2
 #define BOARD_SER1_RTSCTS_DEFAULT 0 // no flow control on UART5 on FMUv1
-#else
+#elif CONFIG_ARCH_BOARD_PX4FMU_V4
+#define BOARD_PWM_COUNT_DEFAULT 6
+#define BOARD_SER1_RTSCTS_DEFAULT 2
+#else // V2
 #define BOARD_PWM_COUNT_DEFAULT 4
 #define BOARD_SER1_RTSCTS_DEFAULT 2
 #endif