Add TXD2 and RXD2 pin definitions (#6989)

Author: Tinyu-Zhao

Diff for: variants/m5stack_atom/pins_arduino.h

@@ -14,10 +14,12 @@
 static const uint8_t TX = 1;
 static const uint8_t RX = 3;
 
+static const uint8_t TXD2 = 32;
+static const uint8_t RXD2 = 26;
+
 static const uint8_t SDA = 26;
 static const uint8_t SCL = 32;
 
-
 static const uint8_t G12 = 12;
 static const uint8_t G19 = 19;
 static const uint8_t G21 = 21;

Diff for: variants/m5stack_fire/pins_arduino.h

@@ -14,6 +14,9 @@
 static const uint8_t TX = 1;
 static const uint8_t RX = 3;
 
+static const uint8_t TXD2 = 17;
+static const uint8_t RXD2 = 16;
+
 static const uint8_t SDA = 21;
 static const uint8_t SCL = 22;
 

Diff for: variants/m5stick_c/pins_arduino.h

@@ -14,6 +14,9 @@
 static const uint8_t TX = 1;
 static const uint8_t RX = 3;
 
+static const uint8_t TXD2 = 33;
+static const uint8_t RXD2 = 32;
+
 static const uint8_t SDA = 32;
 static const uint8_t SCL = 33;