MAINTAINERS: condense some Tegra related entries

There's little point having specific entries in MAINTAINERS for Tegra
drivers that are already covered by the top-level Tegra architecture
support entry, and maintained by people listed there. Remove the
duplicates.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>