accel/rocket: Add job submission IOCTL

Using the DRM GPU scheduler infrastructure, with a scheduler for each
core.

Userspace can decide for a series of tasks to be executed sequentially
in the same core, so SRAM locality can be taken advantage of.

The job submission code was initially based on Panfrost.

v2:
- Remove hardcoded number of cores
- Misc. style fixes (Jeffrey Hugo)
- Repack IOCTL struct (Jeffrey Hugo)

Signed-off-by: Tomeu Vizoso <tomeu@tomeuvizoso.net>