move mechkeys keyboards into the mechkeys/ vendor folder (#15760)

* move mechkeys keyboards to mechkeys/

* fix compilation

* fix default folder

keyboards/mechkeys/acr60/readme.md

@@ -10,11 +10,11 @@ A customizable 60% keyboard made and sold by mechkeys.ca [More info on MECHKEYS]
 
 Make example for this keyboard (after setting up your build environment):
 
-    make acr60:default
+    make mechkeys/acr60:default
 
 Flashing example for this keyboard:
 
-    make acr60:default:flash
+    make mechkeys/acr60:default:flash
 
 To reset the board into bootloader mode, do one of the following:
 

keyboards/mechkeys/alu84/readme.md

@@ -10,11 +10,11 @@ A 75% keyboard made and sold by MECHKEYS.
 
 Make example for this keyboard (after setting up your build environment):
 
-    make alu84:default
+    make mechkeys/alu84:default
 
 Flashing example for this keyboard:
 
-    make alu84:default:flash
+    make mechkeys/alu84:default:flash
 
 To reset the board into bootloader mode, hold Space+B while plugging the cable in.