arch-x86: Fix CPUID function 0

This should return the number of standard features, not the number of
extended features.

Change-Id: Ieb3a36d832cee603f1efd39b4f430b5ac0478561
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/70778
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>

src/arch/x86/cpuid.cc

@@ -162,7 +162,7 @@ namespace X86ISA {
                   ISA *isa = dynamic_cast<ISA *>(tc->getIsaPtr());
                   auto vendor_string = isa->getVendorString();
                   result = CpuidResult(
-                          NumExtendedCpuidFuncs - 1,
+                          NumStandardCpuidFuncs - 1,
                           stringToRegister(vendor_string.c_str()),
                           stringToRegister(vendor_string.c_str() + 4),
                           stringToRegister(vendor_string.c_str() + 8));