numa: Print warning if no node is assigned to a CPU

We need all possible CPUs (including hotplug ones) to be present in the
SRAT when QEMU starts. QEMU already does that correctly today, the only
problem is that when a CPU is omitted from the NUMA configuration, it is
silently assigned to node 0.

Check if all CPUs up to max_cpus are present in the NUMA configuration
and warn about missing CPUs.

Make it just a warning, to allow management software to be updated if
necessary. In the future we may make it a fatal error instead.

Command-line examples:

* Correct, no warning:

  $ qemu-system-x86_64 -smp 2,maxcpus=4
  $ qemu-system-x86_64 -smp 2,maxcpus=4 -numa node,cpus=0-3

* Incomplete, with warnings:

  $ qemu-system-x86_64 -smp 2,maxcpus=4 -numa node,cpus=0
  qemu-system-x86_64: warning: CPU(s) not present in any NUMA nodes: 1 2 3
  qemu-system-x86_64: warning: All CPU(s) up to maxcpus should be described in NUMA config

  $ qemu-system-x86_64 -smp 2,maxcpus=4 -numa node,cpus=0-2
  qemu-system-x86_64: warning: CPU(s) not present in any NUMA nodes: 3
  qemu-system-x86_64: warning: All CPU(s) up to maxcpus should be described in NUMA config

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
v1 -> v2: (no changes)

v2 -> v3:
 * Use enumerate_cpus() and error_report() for error message
 * Simplify logic using bitmap_full()

v3 -> v4:
 * Clarify error message, mention that all CPUs up to
   maxcpus need to be described in NUMA config

v4 -> v5:
 * Commit log update, to make problem description clearer
