elf-ops.h: Add get_elf_note_type()

elf-ops.h: Add get_elf_note_type()

Introduce a routine which, given a pointer to a range of ELF Notes,
searches through them looking for a note matching the type specified
and returns a pointer to the matching ELF note.

get_elf_note_type() is used by elf_load[32|64]() to find the
specified note type required by the 'elf_note_fn' parameter
added in the previous commit.

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