nut: use spaces for all non-recipe whitespace

nut: use spaces for all non-recipe whitespace

To satisfy the CI (because of project style) use spaces instead of tab
in the Makefile, except for Make 'recipes' (which require tabs).

To be consistent do this through the file, no only where CI complained.

There is unusual spacing on the nested define recipes as Make's rules for
those is very particular.

Signed-off-by: Daniel F. Dickinson <redacted>