xen/x86: Don't try to set PCE bit in CR4

xen/x86: Don't try to set PCE bit in CR4

Since VPMU code emulates RDPMC instruction with RDMSR and because hypervisor
does not emulate it there is no reason to try setting CR4's PCE bit (and the
hypervisor will warn on seeing it set).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
(cherry picked from commit 3375d8284dfb7866f261ec008d15d30999ff273b)
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
(cherry picked from commit 07cfc8aee7c0d8976bf945877f11f30755b18896)