KVM: nVMX: Truncate base/index GPR value on address calc in !64-bit

Drop bits 63:32 of the base and/or index GPRs when calculating the
effective address of a VMX instruction memory operand.  Outside of 64-bit
mode, memory encodings are strictly limited to E*X and below.

Fixes: 064aea77 ("KVM: nVMX: Decoding memory operands of VMX instructions")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210422022128.3464144-7-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>