🩹 Fix M907 E-axis check

[thisiskeithb]

Description

While running the build_all_examples script, I found that our Mini Rambo-based CNC config would not build:

details:

In file included from Marlin/src/gcode/feature/digipot/../../../inc/MarlinConfigPre.h:37:0,
                 from Marlin/src/gcode/feature/digipot/../../../inc/MarlinConfig.h:28,
                 from Marlin/src/gcode/feature/digipot/M907-M910.cpp:23:
Marlin/src/gcode/feature/digipot/M907-M910.cpp: In static member function 'static void GcodeSuite::M907_report(bool)':
Marlin/src/gcode/feature/digipot/M907-M910.cpp:137:13: error: 'SP_E_STR' was not declared in this scope
           , SP_E_STR,       stepper.motor_current_setting[2]  // E
             ^

[snip]

*** [.pio/build/rambo/src/src/gcode/feature/digipot/M907-M910.cpp.o] Error 1
============================================================== [FAILED] Took 7.55 seconds ==============================================================

Since there's no extruder on this build/config, using PIN_EXISTS(MOTOR_CURRENT_PWM_E) is not enough and we need to also check for HAS_EXTRUDERS.

Requirements

Mini Rambo board config without an extruder.

Benefits

Mini Rambo board config without an extruder will build.

Configurations

Configurations/config/examples/CNC/miniRambo/

Related Issues

• Add 4 axis CNC configuration for MiniRambo board #26892
• Build All Configurations Status - May 2024 Configurations#1052

[thisiskeithb]

Running a global search for code that uses PIN_EXISTS() macros could probably use some updates now that Marlin can run in all kinds of crazy configurations & varying axis counts, but that's a lot of scope creep that I chose to ignore for now 😁

[thisiskeithb]

Closing since this was fixed through different means in 08fe8a3 / #27087