amdgpu: replace alloca with calloc v2

use heap memory instead of stack memory to avoid potential stack overflow
when a large number of resources are used for the bo_list.

v2: some minor improvement

Signed-off-by: Jammy Zhou <Jammy.Zhou@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>