kmodule: add support for caller specified RootDir
kmodule: add support for caller specified RootDir

Existing genDeps() behaviour checks "/lib/modules" & "/usr/lib/modules"
paths only. This change allows the caller to specify an optional prefix
to the above paths.

Signed-off-by: David Disseldorp <589a549dc9f982d9f46aeeb82a09ab6d87ccf1d8@suse.de>

GanShun/u-root,rminnich/u-root,hugelgupf/u-root,hugelgupf/u-root,hugelgupf/u-root,rminnich/u-root,u-root/u-root,u-root/u-root,rminnich/u-root,GanShun/u-root,rminnich/u-root,u-root/u-root,GanShun/u-root,hugelgupf/u-root