sourceipk.bbclass: Provide the ability to change the source directory
sourceipk.bbclass: Provide the ability to change the source directory

* Allow the directory where the sources are grabbed to be changed.

Signed-off-by: Franklin S. Cooper Jr <b8c01a1703dc362919183054a071c1f348818c23@ti.com>
Signed-off-by: Denys Dmytriyenko <d29de71aea38aad3a87d486929cb0aad173ae612@ti.com>

rcn-ee/meta-arago,MentorEmbedded/meta-arago,rcn-ee/meta-arago,MentorEmbedded/meta-arago,rcn-ee/meta-arago,rcn-ee/meta-arago,MentorEmbedded/meta-arago,rcn-ee/meta-arago,MentorEmbedded/meta-arago