elf: Add optional function ptr to load_elf() to parse ELF notes

This patch adds an optional function pointer, 'elf_note_fn', to
load_elf() which causes load_elf() to additionally parse any
ELF program headers of type PT_NOTE and check to see if the ELF
Note is of the type specified by the 'translate_opaque' arg.
If a matching ELF Note is found then the specfied function pointer
is called to process the ELF note.

Passing a NULL function pointer results in ELF Notes being skipped.

The first consumer of this functionality is the PVHboot support
which needs to read the XEN_ELFNOTE_PHYS32_ENTRY ELF Note while
loading the uncompressed kernel binary in order to discover the
boot entry address for the x86/HVM direct boot ABI.

Signed-off-by: Liam Merwick <liam.merwick@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/ppc/sam460ex.c

@@ -426,7 +426,8 @@ static void sam460ex_init(MachineState *machine)
         if (success < 0) {
             uint64_t elf_entry, elf_lowaddr;
 
-            success = load_elf(machine->kernel_filename, NULL, NULL, &elf_entry,
+            success = load_elf(machine->kernel_filename, NULL,
+                               NULL, NULL, &elf_entry,
                                &elf_lowaddr, NULL, 1, PPC_ELF_MACHINE, 0, 0);
             entry = elf_entry;
             loadaddr = elf_lowaddr;