arch: x86_64: bring back bzImage support

Allow cloud-hypervisor to direct boot the bzImage kernel format using
the regular 32 bit entry point. This can share the memory and vcpu
setup with the regular PVH boot code, but requires the setup of the
'zero page'.

Signed-off-by: Stefan Nuernberger <stefan.nuernberger@cyberus-technology.de>

arch/src/lib.rs

@@ -48,6 +48,10 @@ pub enum Error {
     ModlistSetup(#[source] vm_memory::GuestMemoryError),
     #[error("RSDP extends past the end of guest memory")]
     RsdpPastRamEnd,
+    #[error("Failed to setup Zero Page for bzImage")]
+    ZeroPageSetup(#[source] vm_memory::GuestMemoryError),
+    #[error("Zero Page for bzImage past RAM end")]
+    ZeroPagePastRamEnd,
 }
 
 /// Type for returning public functions outcome.