arch/arm/src/tiva: Add a workaround for tiva with qemu With qemu, tiva_ifup() hangs because ethernet link status can not be set correctly. This PR is a workaround to avoid this issue. Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com> Approved-by: Gregory Nutt <gnutt@nuttx.org>