px4io-v2 Remove GPIO_RC_OUT and vetted RC_IN wiring

Removed the legacy FMUv4 define that was activating a nonexistent
   pull up and on some HW driving the PPM_IN aka RC_IN aka SPEKTRUM_RX
   to VDD.

   Also detailed the connections of this pins for the board.

   The simplest connection is RC_IN to a timer capture pin
   and a UART.
   In this case the UART_RX pin and just be left as is.
   While the pin can be configured as the PPM_IN (Timer capture)
   or as SPEKTRUM_RX_AS_GPIO_OUTPUT to use it as and GPIO to

  Renamed the macros and defines to be more explicit as to what
  Is being done and the sense of the parameters

src/drivers/boards/px4io-v2/board_config.h

@@ -83,12 +83,12 @@
 
 /* Power switch controls ******************************************************/
 
-#define GPIO_SPEKTRUM_PWR_EN (GPIO_OUTPUT|GPIO_CNF_OUTPP|GPIO_MODE_50MHz|GPIO_OUTPUT_SET|GPIO_PORTC|GPIO_PIN13)
-#define POWER_SPEKTRUM(_s)		px4_arch_gpiowrite(GPIO_SPEKTRUM_PWR_EN, (_s))
+#define GPIO_SPEKTRUM_PWR_EN         (GPIO_OUTPUT|GPIO_CNF_OUTPP|GPIO_MODE_50MHz|GPIO_OUTPUT_SET|GPIO_PORTC|GPIO_PIN13)
+#define SPEKTRUM_POWER(_on_true)     px4_arch_gpiowrite(GPIO_SPEKTRUM_PWR_EN, (_on_true))
 
-#define SPEKTRUM_RX_HIGH(_s)	px4_arch_gpiowrite(GPIO_USART1_RX_SPEKTRUM, (_s))
-#define SPEKTRUM_RX_AS_UART()		px4_arch_configgpio(GPIO_USART1_RX)
-#define SPEKTRUM_RX_AS_GPIO()		px4_arch_configgpio(GPIO_USART1_RX_SPEKTRUM)
+#define SPEKTRUM_OUT(_one_true)      px4_arch_gpiowrite(GPIO_USART1_RX_SPEKTRUM, (_one_true))
+#define SPEKTRUM_RX_AS_UART()        px4_arch_configgpio(GPIO_USART1_RX)
+#define SPEKTRUM_RX_AS_GPIO_OUTPUT() px4_arch_configgpio(GPIO_USART1_RX_SPEKTRUM)
 
 #define GPIO_SERVO_FAULT_DETECT (GPIO_INPUT|GPIO_CNF_INPULLUP|GPIO_MODE_INPUT|GPIO_PORTA|GPIO_PIN15)