x86, numa: Add fixed node size option for numa emulation

numa=fake=N specifies the number of fake nodes, N, to partition the
system into and then allocates them by interleaving over physical nodes.
This requires knowledge of the system capacity when attempting to
allocate nodes of a certain size: either very large nodes to benchmark
scalability of code that operates on individual nodes, or very small
nodes to find bugs in the VM.

This patch introduces numa=fake=<size>[MG] so it is possible to specify
the size of each node to allocate.  When used, nodes of the size
specified will be allocated and interleaved over the set of physical
nodes.

FAKE_NODE_MIN_SIZE was also moved to the more-appropriate
include/asm/numa_64.h.

Signed-off-by: David Rientjes <rientjes@google.com>
LKML-Reference: <alpine.DEB.2.00.1002151342510.26927@chino.kir.corp.google.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>