x86: correct PT_NOTE file position

Program and section headers disagreed about the file offset at which
the build ID note lives.

Reported-by: Sylvain Munaut <s.munaut@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/boot/mkelf32.c
+++ b/xen/arch/x86/boot/mkelf32.c
@@ -394,7 +394,7 @@ int main(int argc, char **argv)
         note_phdr.p_paddr   = note_base;
         note_phdr.p_filesz  = note_sz;
         note_phdr.p_memsz   = note_sz;
-        note_phdr.p_offset  = offset;
+        note_phdr.p_offset  = RAW_OFFSET + offset;
 
         /* Tack on the .note\0 */
         out_shdr[2].sh_size += sizeof(out_shstrtab_extra);