editorconfig: Improve verbosity

This commit adds missing `indent_size` configurations for some file
types.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

.editorconfig

@@ -75,6 +75,7 @@ indent_size = 2
 # Makefile
 [Makefile]
 indent_style = tab
+indent_size = 8
 
 # Device tree
 [*.{dts,dtsi,overlay}]
@@ -87,4 +88,5 @@ max_line_length = 75
 
 # Kconfig
 [Kconfig*]
-indent_style=tab
+indent_style = tab
+indent_size = 8