ARM: tegra: remove unused tegra_emc.h

The header file include/linux/platform_data/tegra_emc.h does not seem
to be used anywhere. It was orphaned by a7cbe92c "ARM: tegra: remove
tegra EMC scaling driver". Remove it.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Stephen Warren <swarren@nvidia.com>