KVM: selftests: Add a helper to query if the PMU module param is enabled

Add a helper to probe KVM's "enable_pmu" param, open coding strings in
multiple places is just asking for false negatives and/or runtime errors
due to typos.

Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20240109230250.424295-23-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/include/x86_64/processor.h

@@ -1217,6 +1217,11 @@ static inline uint8_t xsetbv_safe(uint32_t index, uint64_t value)
 
 bool kvm_is_tdp_enabled(void);
 
+static inline bool kvm_is_pmu_enabled(void)
+{
+	return get_kvm_param_bool("enable_pmu");
+}
+
 uint64_t *__vm_get_page_table_entry(struct kvm_vm *vm, uint64_t vaddr,
 				    int *level);
 uint64_t *vm_get_page_table_entry(struct kvm_vm *vm, uint64_t vaddr);