UPSTREAM: arm64: barrier: Restore spec_bar() macro

[ Upstream commit ebfc726e ]

Upcoming errata workarounds will need to use SB from C code. Restore the
spec_bar() macro so that we can use SB.

This is effectively a revert of commit:

  4f30ba1c ("arm64: barrier: Remove spec_bar() macro")

Bug: 342491759
Change-Id: Ib62a0e6c1934c61d6cc46ea412a342dd002bcb5c
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20240508081400.235362-2-mark.rutland@arm.com


Signed-off-by: Will Deacon <will@kernel.org>
[ Mark: trivial backport ]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chunhui Li <chunhui.li@mediatek.com>