[2.0.x] Enable hardware serial ports on LPC1768 (#8004)

* Enable hardware serial ports on LPC1768

* Fix compilation errors with other HALs

* FIx order of includes in LPC1768 HAL main.cpp

* Add support for RX_BUFFER_SIZE and TX_BUFFER_SIZE options in Configuration_adv.h

Marlin/src/gcode/parser.h

@@ -135,7 +135,7 @@ public:
     // Code is found in the string. If not found, value_ptr is unchanged.
     // This allows "if (seen('A')||seen('B'))" to use the last-found value.
     static bool seen(const char c) {
-      const char *p = strchr(command_args, c);
+      char *p = strchr(command_args, c);
       const bool b = !!p;
       if (b) value_ptr = DECIMAL_SIGNED(p[1]) ? &p[1] : (char*)NULL;
       return b;