depmod: Add support for excluding a directory

depmod: Add support for excluding a directory

This adds support to depmod to enable a new exclude directive in
the depmod.d/*.conf configuration file. Currently depmod
already excludes directories named source or build. This change
will allow additional directories like .debug to be excluded also
via a new exclude directive.

depmod.d/exclude.conf example:
exclude	.debug

Signed-off-by: Saul Wold <saul.wold@windriver.com>
[ Fix warnings and make should_exclude_dir() return bool ]
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>