pvh: Introduce EntryPoint struct

In order to properly initialize the kvm regs/sregs structs for
the guest, the load_kernel() return type must specify which
boot protocol to use with the entry point address it returns.

Make load_kernel() return an EntryPoint struct containing the
required information. This structure will later be used
in the vCPU configuration methods to setup the appropriate
initial conditions for the guest.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>

arch/src/lib.rs

@@ -77,4 +77,5 @@ pub mod x86_64;
 #[cfg(target_arch = "x86_64")]
 pub use x86_64::{
     arch_memory_regions, configure_system, layout, layout::CMDLINE_MAX_SIZE, layout::CMDLINE_START,
+    BootProtocol, EntryPoint,
 };