drm/amdgpu: rework sched_list generation

Generate HW IP's sched_list in amdgpu_ring_init() instead of
amdgpu_ctx.c. This makes amdgpu_ctx_init_compute_sched(),
ring.has_high_prio and amdgpu_ctx_init_sched() unnecessary.
This patch also stores sched_list for all HW IPs in one big
array in struct amdgpu_device which makes amdgpu_ctx_init_entity()
much more leaner.

v2:
fix a coding style issue
do not use drm hw_ip const to populate amdgpu_ring_type enum

v3:
remove ctx reference and move sched array and num_sched to a struct
use num_scheds to detect uninitialized scheduler list

v4:
use array_index_nospec for user space controlled variables
fix possible checkpatch.pl warnings

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>