Fix RAK3401 SKY66122-11 FEM control: enable CSD/CPS for proper PA and LNA operation

The RAK13302 1W module uses a Skyworks SKY66122-11 front-end module with
three digital control pins (CSD, CTX, CPS) that must be actively driven
by the host MCU. The previous code only managed CTX (GPIO 31) — toggling
it for TX/RX — but never initialized CSD (GPIO 24) or CPS (GPIO 21),
leaving them floating with no pull-up/pull-down resistors on the PCB.

With floating CSD and CPS, the SKY66122 was in an undefined operating
mode:
- The 30 dB TX PA may not have been reliably engaging
- The 16 dB RX LNA was never reliably active, degrading receive
sensitivity

variants/rak3401/variant.h

@@ -147,8 +147,14 @@ static const uint8_t AREF = PIN_AREF;
 #define SX126X_BUSY (9)
 #define SX126X_RESET (4)
 
-#define SX126X_POWER_EN (21)
-// DIO2 controlls an antenna switch and the TCXO voltage is controlled by DIO3
+// SKY66122-11 FEM control pins (active HIGH, active LOW = shutdown <1uA)
+// CSD+CPS must be HIGH for TX and RX; CTX selects TX(HIGH) vs RX(LOW)
+// CTX also enables the 5V boost converter for the PA during TX
+#define P_LORA_PA_CSD (24)          // P0.24 -> SKY66122 CSD (pin 11) - FEM enable
+#define SX126X_POWER_EN (21)        // P0.21 -> SKY66122 CPS (pin 1) - path select
+#define P_LORA_PA_EN  (31)          // P0.31 -> SKY66122 CTX (pin 2) - TX/RX + boost EN
+
+// DIO2 has a NC 0R footprint (R25) to CTX; not connected by default
 #define SX126X_DIO2_AS_RF_SWITCH
 #define SX126X_DIO3_TCXO_VOLTAGE 1.8
 
@@ -159,7 +165,6 @@ static const uint8_t AREF = PIN_AREF;
 #define P_LORA_DIO_1 SX126X_DIO1
 #define P_LORA_BUSY SX126X_BUSY
 #define P_LORA_RESET SX126X_RESET
-#define P_LORA_PA_EN  31
 
 // enables 3.3V periphery like GPS or IO Module
 // Do not toggle this for GPS power savings