kvm tools: Remove KVM_NR_CPUS

The KVM_NR_CPUS define is only really used to statically size the global
kvm_cpus array, which can just as easily be allocated on startup.  There is
some checking of the -c <nr cpus> value given against NR_CPUs but this is
later again checked against a dynamically-determined limit from
KVM_CAP_MAX_VCPUS anyway.  The hardwired limit is arbitrary and not strictly
necessary.

This patch removes the #define, replacing the statically-sized array with
a malloc; the array is kvm->nrcpus+1 in size so that any iterator can halt
at the end (this is done in kvm_cpu__reboot, which doesn't have access to
a struct kvm* and therefore kvm->nrcpus).

An unused #define in x86/mptable.c is also removed.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Pekka Enberg <penberg@kernel.org>