[PATCH] Add maxvcpus support

[Michal Novotny <minovotn@redhat.com>]

Hi,
this is patch to add maxvcpus support to xen xm command. It's using 
vcpu_avail bitmask and sets the number of vcpus to maxvcpus if present. 
If it's not present, old behavior is preserved.

In domain config file you can define it as follows:

  maxvcpus = 4
  vcpus = 2

this automatically sets vcpus to 4 and corresponding bitmask to present 
2 vcpus in the guest with option to increase it up to 4 vcpus. If 
maxvcpus is not present, the old behavior for vcpus is preserved, ie. 
you can set vcpus to some number of vcpus to be used and the vcpu_avail 
is set appropriately to use all of them. Only when you use maxvcpus and 
vcpus new vcpu_avail value is calculated to show PV guest the desired 
number of vcpus only.

It's been tested using RHEL-5 32-bit PV guest with maxvcpus = 4 and 
vcpus = 2 and also the previous setup of vcpus = 2 only... In both cases 
I was able to use 'xm vcpu-set {domainId} {numberOfVCPUs}' to increase 
move vcpu count from 0 to maxvcpus/vcpus so it was working as designed.

Michal

Signed-off-By: Michal Novotny<minovotn@redhat.com>