KVM: selftests: use unified time type for comparison

With test case kvm_page_table_test, start time is acquired with
time type CLOCK_MONOTONIC_RAW, however end time in timespec_elapsed()
is acquired with time type CLOCK_MONOTONIC. This can cause inaccurate
elapsed time calculation due to mixing timebases, e.g. LoongArch in
particular will see weirdness.

Modify kvm_page_table_test to use unified time type CLOCK_MONOTONIC for
start time.

Signed-off-by: Bibo Mao <[e-mail]>
Reviewed-by: Oliver Upton <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
[sean: massage changelog]
Signed-off-by: Sean Christopherson <[e-mail]>

tools/testing/selftests/kvm/kvm_page_table_test.c

···
 		if (READ_ONCE(host_quit))
 			return NULL;
 
-		clock_gettime(CLOCK_MONOTONIC_RAW, &start);
+		clock_gettime(CLOCK_MONOTONIC, &start);
 		ret = _vcpu_run(vcpu);
 		ts_diff = timespec_elapsed(start);
 
···
 	/* Test the stage of KVM creating mappings */
 	*current_stage = KVM_CREATE_MAPPINGS;
 
-	clock_gettime(CLOCK_MONOTONIC_RAW, &start);
+	clock_gettime(CLOCK_MONOTONIC, &start);
 	vcpus_complete_new_stage(*current_stage);
 	ts_diff = timespec_elapsed(start);
 
···
 
 	*current_stage = KVM_UPDATE_MAPPINGS;
 
-	clock_gettime(CLOCK_MONOTONIC_RAW, &start);
+	clock_gettime(CLOCK_MONOTONIC, &start);
 	vcpus_complete_new_stage(*current_stage);
 	ts_diff = timespec_elapsed(start);
 
···
 
 	*current_stage = KVM_ADJUST_MAPPINGS;
 
-	clock_gettime(CLOCK_MONOTONIC_RAW, &start);
+	clock_gettime(CLOCK_MONOTONIC, &start);
 	vcpus_complete_new_stage(*current_stage);
 	ts_diff = timespec_elapsed(start);