Added missing SX126x/8x SPI slowdown on Apollo3

src/BuildOpt.h

@@ -148,6 +148,9 @@
     #define RADIOLIB_SOFTWARE_SERIAL_UNSUPPORTED
     #define RADIOLIB_HARDWARE_SERIAL_PORT               Serial1
 
+    // slow down SX126x/8x SPI on this platform
+    #define RADIOLIB_SPI_SLOWDOWN
+
   #elif defined(SAMD_SERIES)
     // Adafruit SAMD boards (M0 and M4)
     #define RADIOLIB_PLATFORM                           "Adafruit SAMD"
@@ -163,6 +166,9 @@
     #define RADIOLIB_SOFTWARE_SERIAL_UNSUPPORTED
     #define RADIOLIB_HARDWARE_SERIAL_PORT               Serial1
 
+    // slow down SX126x/8x SPI on this platform
+    #define RADIOLIB_SPI_SLOWDOWN
+
   #elif defined(ARDUINO_ARCH_SAMD)
     // Arduino SAMD (Zero, MKR, etc.)
     #define RADIOLIB_PLATFORM                           "Arduino SAMD"
@@ -251,6 +257,9 @@
     // Apollo3 uses mbed libraries, which already contain ESP8266 driver
     #define RADIOLIB_EXCLUDE_ESP8266
 
+    // slow down SX126x/8x SPI on this platform
+    #define RADIOLIB_SPI_SLOWDOWN
+
   #elif defined(ARDUINO_ARDUINO_NANO33BLE)
     // Arduino Nano 33 BLE
     #define RADIOLIB_PLATFORM                           "Arduino Nano 33 BLE"