KVM: selftests: Add X86_FEATURE_PAE and use it calc "fallback" MAXPHYADDR

Add X86_FEATURE_PAE and use it to guesstimate the MAXPHYADDR when the
MAXPHYADDR CPUID entry isn't supported.

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221006005125.680782-2-seanjc@google.com

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

@@ -89,6 +89,7 @@ struct kvm_x86_cpu_feature {
 #define	X86_FEATURE_XSAVE		KVM_X86_CPU_FEATURE(0x1, 0, ECX, 26)
 #define	X86_FEATURE_OSXSAVE		KVM_X86_CPU_FEATURE(0x1, 0, ECX, 27)
 #define	X86_FEATURE_RDRAND		KVM_X86_CPU_FEATURE(0x1, 0, ECX, 30)
+#define X86_FEATURE_PAE			KVM_X86_CPU_FEATURE(0x1, 0, EDX, 6)
 #define	X86_FEATURE_MCE			KVM_X86_CPU_FEATURE(0x1, 0, EDX, 7)
 #define	X86_FEATURE_APIC		KVM_X86_CPU_FEATURE(0x1, 0, EDX, 9)
 #define	X86_FEATURE_CLFLUSH		KVM_X86_CPU_FEATURE(0x1, 0, EDX, 19)

tools/testing/selftests/kvm/lib/x86_64/processor.c

@@ -1012,12 +1012,10 @@ bool is_amd_cpu(void)
 void kvm_get_cpu_address_width(unsigned int *pa_bits, unsigned int *va_bits)
 {
 	const struct kvm_cpuid_entry2 *entry;
-	bool pae;
 
 	/* SDM 4.1.4 */
 	if (kvm_get_cpuid_max_extended() < 0x80000008) {
-		pae = kvm_get_supported_cpuid_entry(1)->edx & (1 << 6);
-		*pa_bits = pae ? 36 : 32;
+		*pa_bits == kvm_cpu_has(X86_FEATURE_PAE) ? 36 : 32;
 		*va_bits = 32;
 	} else {
 		entry = kvm_get_supported_cpuid_entry(0x80000008);