riscv: qspinlock: Use new static key for controlling call of virt_spin_lock()

Add a static key controlling whether virt_spin_lock() should be
called or not. When running on bare metal set the new key to
false.

The KVM guests fall back to a Test-and-Set spinlock, because fair
locks have horrible lock 'holder' preemption issues. The
virt_spin_lock_key would shortcut for the
queued_spin_lock_slowpath() function that allow virt_spin_lock to
hijack it.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>