LoongArch: KVM: Check kvm_request_pending() in kvm_late_check_requests()

LoongArch: KVM: Check kvm_request_pending() in kvm_late_check_requests()

Add kvm_request_pending() checking firstly in kvm_late_check_requests(),
at most time there is no pending request, then the following pending bit
checking can be skipped.

Also embed function kvm_check_pmu() in to kvm_late_check_requests(), and
put it after the kvm_request_pending() checking.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>