arm64: vdso: Annotate for BTI

Generate BTI annotations for all assembly files included in the 64 bit
vDSO.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20200506195138.22086-10-broonie@kernel.org


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