arm64: vdso: Use only one single vvar mapping

arm64: vdso: Use only one single vvar mapping

The vvar mapping is the same for all processes. Use a single mapping to
simplify the logic and align it with the other architectures.

In addition this will enable the move of the vvar handling into generic code.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Will Deacon <will@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/all/20241010-vdso-generic-base-v1-5-b64f0842d512@linutronix.de