ARM: tegra: Restore memory arbitration on resume from LP1 on Tegra30+

The external memory arbitration configuration is getting reset after
memory entering into self-refresh mode, it shall be restored on the
exit. Note that MC_EMEM_ARB_CFG register is shadowed and latching
happens on the EMC timing update. This fixes 2x GPU performance
degradation after resuming from LP1 on Tegra30.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>