BACKPORT: arm64: mm: Mark .rodata as RO

Currently the .rodata section is actually still executable when DEBUG_RODATA
is enabled. This changes that so the .rodata is actually read only, no execute.
It also adds the .rodata section to the mem_init banner.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
[catalin.marinas@arm.com: added vm_struct vmlinux_rodata in map_kernel()]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Bug: 31374226
Change-Id: I6fd95beaf814fc91805da12c5329a57ce9008fd7
(cherry picked from commit 2f39b5f9)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>