x86-64, NUMA: Unify use of memblk in all init methods

Make both amd and dummy use numa_add_memblk() to describe the detected
memory blocks.  This allows initmem_init() to call
numa_register_memblk() regardless of init method in use.  Drop custom
memory registration codes from amd and dummy.

After this change, memblk merge/cleanup in numa_register_memblks() is
applied to all init methods.

As this makes compute_hash_shift() and numa_register_memblks() used
only inside numa_64.c, make them static.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Shaohui Zheng <shaohui.zheng@intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: H. Peter Anvin <hpa@linux.intel.com>