hypervisor: Start moving register definitions to the hypervisor crate

Most of arch/src/x86_64/regs.rs will eventually move unde
hypervisor/src/x86/regs.rs.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

hypervisor/src/arch/x86/mod.rs

@@ -63,3 +63,5 @@ pub enum Exception {
     VE = 20, // Virtualization Exception
     CP = 21, // Control Protection Exception
 }
+
+pub mod regs;