radeon: use kvcalloc for relocs and chunks

kvmalloc_array + __GFP_ZERO is the same with kvcalloc.

As for p->chunks, it will be used in:
```
if (ib_chunk->kdata)
		memcpy(parser->ib.ptr, ib_chunk->kdata, ib_chunk->length_dw * 4);
```

If chunks doesn't zero out with __GFP_ZERO, it may point to somewhere else, e.g.,
```
Unable to handle kernel paging request at virtual address 0000000000010000
...
pc is at memcpy+0x84/0x250
ra is at radeon_cs_ioctl+0x368/0xb90 [radeon]
```

after allocating chunks with __GFP_KERNEL/kvcalloc, this bug is fixed.
Fixes: 3fcb4f01 ("drm/radeon: Use kvmalloc for CS chunks")
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Chen Li <chenli@uniontech.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>