[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/inc/SanityCheck.h

@@ -235,6 +235,24 @@
   #error "WEBSITE_URL must be specified."
 #endif
 
+/**
+ * Serial
+ */
+#ifndef USBCON
+  #if ENABLED(SERIAL_XON_XOFF) && RX_BUFFER_SIZE < 1024
+    #error "XON/XOFF requires RX_BUFFER_SIZE >= 1024 for reliable transfers without drops."
+  #endif
+
+  #if !IS_POWER_OF_2(RX_BUFFER_SIZE) || RX_BUFFER_SIZE < 2
+    #error "RX_BUFFER_SIZE must be a power of 2 greater than 1."
+  #endif
+
+  // 256 is the max limit due to uint8_t head and tail. Use only powers of 2. (...,16,32,64,128,256)
+  #if TX_BUFFER_SIZE && (TX_BUFFER_SIZE < 2 || TX_BUFFER_SIZE > 256 || !IS_POWER_OF_2(TX_BUFFER_SIZE))
+    #error "TX_BUFFER_SIZE must be 0 or a power of 2 greater than 1."
+  #endif
+#endif
+
 /**
  * Dual Stepper Drivers
  */