gpu: host1x: Add host1x driver

Add host1x, the driver for host1x and its client unit 2D. The Tegra
host1x module is the DMA engine for register access to Tegra's
graphics- and multimedia-related modules. The modules served by
host1x are referred to as clients. host1x includes some other
functionality, such as synchronization.

Signed-off-by: Arto Merilainen <amerilainen@nvidia.com>
Signed-off-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-by: Thierry Reding <thierry.reding@avionic-design.de>
Tested-by: Thierry Reding <thierry.reding@avionic-design.de>
Tested-by: Erik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>