soc/tegra: pmc: restrict compilation of suspend-related support to ARM

soc/tegra: pmc: restrict compilation of suspend-related support to ARM

Tegra SoCs with 64-bit ARM support don't currently support deep CPU
low-power states in mainline Linux.  When this support is added in the
future, it will probably look rather different from the existing
32-bit ARM support, since the ARM64 maintainers' strong preference is
to use PSCI to implement it.

So, for the time being, prevent the CPU suspend-related code and data
in the Tegra PMC driver from compiling on ARM64.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Paul Walmsley <pwalmsley@nvidia.com>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Allen Martin <amartin@nvidia.com>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Alexandre Courbot <gnurou@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>