drm/panthor: Add the driver frontend block

This is the last piece missing to expose the driver to the outside
world.

This is basically a wrapper between the ioctls and the other logical
blocks.

v6:
- Add Maxime's and Heiko's acks
- Return a page-aligned BO size to userspace
- Keep header inclusion alphabetically ordered

v5:
- Account for the drm_exec_init() prototype change
- Include platform_device.h

v4:
- Add an ioctl to let the UMD query the VM state
- Fix kernel doc
- Let panthor_device_init() call panthor_device_init()
- Fix cleanup ordering in the panthor_init() error path
- Add Steve's and Liviu's R-b

v3:
- Add acks for the MIT/GPL2 relicensing
- Fix 32-bit support
- Account for panthor_vm and panthor_sched changes
- Simplify the resv preparation/update logic
- Use a linked list rather than xarray for list of signals.
- Simplify panthor_get_uobj_array by returning the newly allocated
  array.
- Drop the "DOC" for job submission helpers and move the relevant
  comments to panthor_ioctl_group_submit().
- Add helpers sync_op_is_signal()/sync_op_is_wait().
- Simplify return type of panthor_submit_ctx_add_sync_signal() and
  panthor_submit_ctx_get_sync_signal().
- Drop WARN_ON from panthor_submit_ctx_add_job().
- Fix typos in comments.

Co-developed-by: Steven Price <[email protected]>
Signed-off-by: Steven Price <[email protected]>
Signed-off-by: Boris Brezillon <[email protected]>
Acked-by: Steven Price <[email protected]> # MIT+GPL2 relicensing,Arm
Acked-by: Grant Likely <[email protected]> # MIT+GPL2 relicensing,Linaro
Acked-by: Boris Brezillon <[email protected]> # MIT+GPL2 relicensing,Collabora
Reviewed-by: Steven Price <[email protected]>
Reviewed-by: Liviu Dudau <[email protected]>
Acked-by: Maxime Ripard <[email protected]>
Acked-by: Heiko Stuebner <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]