[POWERPC] bootwrapper: Allow wrapper script to execute verbosely

Allow wrapper script to print verbose progress when the V is set in the
environment.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>