sgi/prepare-fedora-disk: switch to using generic platform name instead of sgi

To adapt to the product names for the latest SGI platforms, replace the use
of 'sgi' with 'refinfra' where applicable. This change affects the buid test
scripts of ras and kvm. So update these scripts as well.

Change-Id: I368992a25feae4260e6c5368621126d929653f47
Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>