net: sni_netsec: Add workaround for timeout error

net: sni_netsec: Add workaround for timeout error

The NETSEC GMAC occasionally falls into a weird state where
MAC_REG_DESC_SOFT_RST has never been cleared and shows errors like the
below when networking commands are issued:

    => ping 192.168.1.1
    ethernet@522d0000 Waiting for PHY auto negotiation to complete... done
    netsec_wait_while_busy: timeout
    Using ethernet@522d0000 device

    ARP Retry count exceeded; starting again
    ping failed; host 192.168.1.1 is not alive

It happens on not only 'ping' but also 'dhcp', 'tftp' and so on.

Luckily, restarting the NETSEC GMAC and trying again seems to fix the
problematic state. So first ensure that we haven't entered the state by
checking MAC_REG_DESC_SOFT_RST to be cleared; otherwise, restarting
NETSEC/PHY and trying again would work as a workaround.

Signed-off-by: Ryosuke Saito <ryosuke.saito@linaro.org>
Tested-by: Masahisa Kojima <masahisa.kojima@linaro.org>