arm64: mm: Mark executable text as guarded pages

When the kernel is built for BTI and running on a system which supports
make all executable text guarded pages to ensure that loadable module
and JITed BPF code is protected by BTI.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20200506195138.22086-7-broonie@kernel.org


Signed-off-by: Will Deacon <will@kernel.org>