ARM: tegra: defconfig fixes

The AK8975 Kconfig option was renamed during the 3.10 merge window.
Adjust tegra_defconfig to enable the new name, so it's not missing
useful features.

Tegra DRM support used to be enabled in the default Tegra configuration,
but it now depends on CONFIG_TEGRA_HOST1X which is disabled by default.
Enable CONFIG_TEGRA_HOST1X so that DRM support is compiled in again.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
[swarren, squashed Alex's and my changes together]
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>