MAINTAINERS: add Alexandre Courbot for Tegra

I'd like to propose Alexandre Courbot as an additional Tegra maintainer.
He's been working on a variety of Tegra-related code for a while, and
is now officially tasked with working on upstream support.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
--
v2:
* Use Alexandre's full name.
* Use a non-NVIDIA email address to avoid Exchange Server patch corruption.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>