iommu: arm-smmu: Program TTBR1 to a zero page

It was observed that address translation was occurring on TTBR1 even
with TCR.EPD1 set. Program TTBR1 to a valid zero page to get a S1
fault instead of a S2 fault.

Change-Id: I06dcd1a0b9f6636812ff8d25528ce1c37663ea5c
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>