x86/kmsan: Don't call instrumented code from kmsan_virt_addr_valid()

kmsan_virt_addr_valid()改用preempt_disable_notrace()与__pfn_valid()验证PFN，退出用preempt_enable_no_resched_notrace()；避免DEBUG_PREEMPT下插桩preempt_count_add触发递归。