ARM: tegra: only run PL310 init on systems with one

Fix tegra_init_cache() to check whether the system has a PL310 cache
before touching the PL310 registers. This prevents access to non-existent
registers on Tegra114 and later.

Note for stable kernels:
In <= v3.12, the file to patch is arch/arm/mach-tegra/common.c.

Cc: <stable@vger.kernel.org> # v3.9+
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>