RISC-V: paravirt: pvqspinlock: Add kconfig entry

Add kconfig entry for paravirt_spinlock, an unfair qspinlock
virtualization-friendly backend, by halting the virtual CPU rather
than spinning.

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