packaged-staging: enhancements from Poky for fetching and relocatability

packaged-staging: enhancements from Poky for fetching and relocatability

Firstly adds tooling from Poky to scan packages and fix up paths in libtool
files, we then build on this to further post-process native packages (native,
cross, sdk) and fix up any references to the STAGING_DIR in non-binary files.

Secondly adds support for fetching packaged staging packages from a mirror by
setting PSTAGE_MIRROR to point to the root of a pstaging directory.

Signed-off-by: Joshua Lock <josh@linux.intel.com>