Fix for R.D.F.G.S.C. with MEGATRONICS 3 board

[thinkyhead]

Rebase, cleanup of #4441, addressing #4439

When #4408 added support for RepRapWorld LCD, it improperly overrode the pins for other LCDs like the REPRAP_DISCOUNT_FULL_GRAPHIC_SMART_CONTROLLER. This PR restores those pin definitions.

[Blue-Marlin]

The same is needed for Minitronics

[thinkyhead]

@Blue-Marlin Oh yes?? Can we also further add support for the RDFGSC (because currently the Minitronics pins defines all its LCD pins as -1). Do we know whether the same pins will work for this unit as for the Megatronics 3?

Also, do you think we should define these other pins in all cases? :

  #define BLEN_C 2
  #define BLEN_B 1
  #define BLEN_A 0

At one point I recall (maybe only in dev?) moving the definitions for these three out of the pins files, because they are always defined as 0, 1, 2.

[Blue-Marlin]

I have no clue, but the structural changes, for Minitronics, in #4408 have been the same.

As far i can see the BLEN_? definitions can be removed from the Configs. They are defined as well in ultralcd_implementation_hitachi_HD44780.h as indogm_lcd_implementation.h for all ULTIPANEL aka panels that can handle a menu because they have an input device.

[thinkyhead]

the BLEN_? definitions can be removed from the Configs

Yes indeed. Actually, the ultralcd headers are a little convoluted concerning these bits. I'm trying to sort them out so there's no unnecessary redundancy.