Allow PGOOD polling interval of 500ms

The code has an explicit check for a minimum allowed
PGOOD polling interval.  Decrease that from 1s to 500ms
as there are new requirements on a specific system
to poll at the 500ms.

Change-Id: If42ecc9244b5e0d8d5b5c17275241f820537d34a
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
1 file changed