tegra: Remove unused IOCTL implementations

The DRM_TEGRA_GEM_{GET,SET}_FLAGS and DRM_TEGRA_GEM_{GET,SET}_TILING
IOCTLs were badly designed and have since been obsoleted by framebuffer
modifiers. Remove these implementations to make it clear their usage is
discouraged.

Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>