DWIN support for platforms other than STM32F1

[jvandervyver]

Requirements

None, this change should be fully backward compatible with existing working implementations

Description

I have a Ender 3 V2 and SKR1.4 Turbo. I was able to get it working, but I'm hoping I won't need to repeatedly merge my changes back in.

If my changes are not according to standards, give me code review feedback and I can make the changes required :)

Benefits

• Allows using LCD_SERIAL_PORT for Creality DWIN display
• Creality DWIN screen jumps from some screens to other without reason. For example, setting the hotend temperature would jump inadvertently to the Print options screen. To resolve this, I fixed the warnings, namely that an unsigned was being compared to a signed value (ie. char). That was probably what caused this issue. However I also replaced auto because it doesn't appear to conform to the Do use modern C++11 features

Configurations

I used the standard Ender 3 v2 configuration. Additionally I made the following change to pins_BTT_SKR_V1_4.h:

#if ENABLED(DWIN_CREALITY_LCD)
  // RET6 DWIN ENCODER LCD
  #define BTN_ENC                           P1_20
  #define BTN_EN1                           P1_23
  #define BTN_EN2                           P1_22

  #ifndef BEEPER_PIN
    #define BEEPER_PIN                      P1_21
    #undef SPEAKER
  #endif
#endif

Related Issues

Not fully aware of another issue