x86: remove depends on X86_32 from PARAVIRT & PARAVIRT_GUEST

With this, the paravirt_ops code can be enabled on x86_64 also.

Each guest implementation (Xen, VMI, lguest) now depends on X86_32. The
dependencies can be dropped for each one when they start to support
x86_64.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>