xen: arm: Add support for the Exynos secure firmware

xen: arm: Add support for the Exynos secure firmware

The existence of secure firmware is dictated by the presence of
"samsung,secure-firmware" in the DT.

The Arndale board does not have that entry, and uses the address as defined
in "samsung,exynos4210-sysram", offset 0 as the smp init address. This is
possibly true for all SoCs without secure firmware.

For other boards which do have a "secure-firmware" node, use sysram-ns
at offset +0x1c as the smp init address.

The "secure-firmware" MMIO range contains ways to idle the CPU. As this gets
mapped to DOM0 because of its presence in the DT, we blacklist it.

Have tested this on the Odroid XU. I have also tested the other code path
on the Odroid XU by removing "secure-firmware" from its DT. I could see
that the other code path was exercised with correct smp init address
values.

Signed-off-by: Suriyan Ramasami <suriyan.r@gmail.com>
Tested-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>