ARM: tegra: remove TEGRA_EMC_SCALING_ENABLE

Commit a7cbe92c ("ARM: tegra: remove tegra EMC scaling driver")
removed the only user of TEGRA_EMC_SCALING_ENABLE. Remove its Kconfig
entry too.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>