x86: change paravirt_32.c name

This patch changes paravirt_32.c to paravirt.c. The goal
is to have paravirt support in x86_64, so we do it in a common file

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>