u-boot-lsi: Add do_get_tag() compiling step

- To get the source tag, add new python function do_get_tag() as
compiling step after do_patch, before do_build.
- Update SRCREV to tag 5.8.1.43 for lsi-v2013.01.01 branch
- Update SRCREV to tag 4.8.1.90 for lsi-v2010.03 branch

Signed-off-by: Paul Butler <paul.butler@windriver.com>