x86/atomics: Always inline arch_atomic64*()

As already done for regular arch_atomic*(), always inline arch_atomic64*().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230126151323.585115019@infradead.org