userportal, webadmin: don't enable balloon on ppc arch (part2)

The memory ballooning doesn't work on ppc so neither portal
nor admin should allow to set it. This patch fixes problem
introduced by the first patch which prevents user from enabling
the baloon on x86 arch.

Bug-Url: https://bugzilla.redhat.com/1127677
Change-Id: Iea925ae11f1a05e857e102e932876d8b5a9fb0fc
Signed-off-by: Jiri Moskovcak <jmoskovc@redhat.com>