[rhel6-branch] check size of ppc64.img

[David Cantrell]

Check the size of ppc64.img in addition to initrd.img to see if it's greater
than 32M.  This script is a minefield, so anything that looks redundant or
extra, I prefer to not change.

Related to 1006043.  Another patch coming to reduce the size of ppc64.img once
feedback is received from IBM Australia.