post-image: show each script filename before execution

This also simplifies code by removing the ifneq/endif clauses.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>