x86: msr: Don't test bits 63:32 of SYSENTER MSRs on 32-bit builds

Squish the "address" stuffed into SYSENTER_EIP/ESP into an unsigned long
so as to drop bits 63:32 on 32-bit builds.  VMX diverges from bare metal
in the sense that the associated VMCS fields are natural width fields,
whereas the actual MSRs hold 64-bit values, even on CPUs that don't
support 64-bit mode.  This causes the tests to fail if bits 63:32 are
non-zero and a VM-Exit/VM-Enter occurs on and/or between WRMSR/RDMSR,
e.g. when running the tests in L1 or deeper.

Don't bother trying to actually test that bits 63:32 are dropped, the
behavior depends on the (virtual) CPU capabilities, not the build, and
the behavior is specific to VMX as both SVM and bare metal preserve the
full 64-bit values.  And because practically no one cares about 32-bit
KVM, let alone an obscure architectural quirk that doesn't affect real
world kernels.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200428231135.12903-1-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>