ARM: tegra: make tegra_cpu_reset_handler_enable() __init

This solves a section mismatch warning. I hadn't noticed this before,
because my compiler was inlining tegra_cpu_reset_handler_enable() inside
tegra_cpu_reset_handler_init(), which is already __init, but I switched
compilers and it stopped doing that.

Cc: <stable@kernel.org> # v3.4
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>