amdkfd: Add amdkfd skeleton driver

This patch adds the amdkfd skeleton driver. The driver does nothing except
define a /dev/kfd device.

It returns -ENODEV on all amdkfd IOCTLs.

v3: Move bool field to the end of structure, removed the pmc ioctls and added
a meaningful error message for ioctl error.

v5:

Create a new folder drm/amd and move amdkfd from drm/radeon/ to drm/amd/
Remove scheduler_class from kfd_priv.h as it was never used
Add skeleton implementation of the Get Version IOCTL

v6:
Update module version to the correct number and remove the "default m" from the
Kconfig file

Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>