build: Track explicit module dependencies in Makefile.core.def

Add a new keyword, "depends", to the module definition syntax
used in Makefile.core.def. This allows specifying explicit module
dependencies together with the module definition.

Do not track the "extra_deps.lst" file in the repository anymore,
it is now auto-generated.

Make use of this new keyword in the bli module definition.

Signed-off-by: Oliver Steffen <osteffen@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

.gitignore

@@ -11,7 +11,6 @@
 *.img
 *.log
 *.lst
-!/grub-core/extra_deps.lst
 *.marker
 *.mod
 *.o