x86/head: Make empty_zero_page read-only

This makes the zero page read-only.  It should have essentially no
overhead because it lives in the shiny new .robss..page_aligned
section.

While I'm at it, use ENDOBJECT to make the objdump output nicer.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
2 files changed