ARM: 8597/1: VDSO: put RO and RO after init objects into proper sections

vdso_data_mapping is never modified, so mark it as const.

vdso_total_pages, vdso_data_page, vdso_text_mapping and cntvct_ok are
initialized by vdso_init(), thereafter are read only.

The fact that they are read only after init makes them candidates for
__ro_after_init declarations.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Nathan Lynch <nathan_lynch@mentor.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>