u-boot-lsi: Update SRCREV to tag to 5.8.1.44 and 4.8.1.91

- Update SRCREV to tag to 5.8.1.44 for lsi-v2013.01.01 branch
- Update SRCREV to tag to 4.8.1.91 for lsi-v2010.03 branch
- Set default UBOOT_SUFFIX to "img"

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