x86/alternatives: Fix section mismatch warnings

Fix stuff like:

  WARNING: modpost: vmlinux.o: section mismatch in reference: \
  __optimize_nops (section: .text) -> debug_alternative (section: .init.data)

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230513160146.16039-1-bp@alien8.de