HAL and serial cleanup

Co-Authored-By: Jason Smith <20053467+sjasonsmith@users.noreply.github.com>

Marlin/src/HAL/STM32F1/HAL.h

@@ -53,7 +53,7 @@
 // ------------------------
 
 #ifndef STM32_FLASH_SIZE
-  #if defined(MCU_STM32F103RE) || defined(MCU_STM32F103VE)
+  #if EITHER(MCU_STM32F103RE, MCU_STM32F103VE)
     #define STM32_FLASH_SIZE 512
   #else
     #define STM32_FLASH_SIZE 256
@@ -106,9 +106,6 @@
   #else
     #error "SERIAL_PORT_2 must be from -1 to 5. Please update your configuration."
   #endif
-  #define NUM_SERIAL 2
-#else
-  #define NUM_SERIAL 1
 #endif
 
 #ifdef DGUS_SERIAL

Marlin/src/HAL/STM32F1/MarlinSerial.h

@@ -30,6 +30,7 @@
   #include "../../feature/e_parser.h"
 #endif
 
+// Increase priority of serial interrupts, to reduce overflow errors
 #define UART_IRQ_PRIO 1
 
 class MarlinSerial : public HardwareSerial {

Marlin/src/HAL/STM32F1/sdio.cpp

@@ -26,7 +26,7 @@
 
 #include "../../inc/MarlinConfig.h" // Allow pins/pins.h to set density
 
-#if defined(STM32_HIGH_DENSITY) || defined(STM32_XL_DENSITY)
+#if EITHER(STM32_HIGH_DENSITY, STM32_XL_DENSITY)
 
 #include "sdio.h"