KVM/nVMX: Use __vmx_vcpu_run in nested_vmx_check_vmentry_hw

Replace inline assembly in nested_vmx_check_vmentry_hw
with a call to __vmx_vcpu_run.  The function is not
performance critical, so (double) GPR save/restore
in __vmx_vcpu_run can be tolerated, as far as performance
effects are concerned.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Reviewed-and-tested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
[sean: dropped versioning info from changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20201231002702.22237077-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>