arm64: kconfig: Ensure spinlock fastpaths are inlined if !PREEMPT

When running with CONFIG_PREEMPT=n, the spinlock fastpaths fit inside
64 bytes, which typically coincides with the L1 I-cache line size.

Inline the spinlock fastpaths, like we do already for rwlocks.

Signed-off-by: Will Deacon <will.deacon@arm.com>