x86: move .altinstr_replacement past _einittext

x86: move .altinstr_replacement past _einittext

This section's contents do not represent part of actual hypervisor text,
so shouldn't be included in what is_kernel_inittext() or (while still
booting) is_active_kernel_text() report "true" for. Keep them in
.init.text though, as there's no real reason to have a separate section
for this in the final binary.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>