Revert "SMC911x driver fixed for NFS boot"

Revert "SMC911x driver fixed for NFS boot"

This reverts commit ca9c8a1e10fac01e6a1129f82a7ce18bd818fa43,
which causes compile warnings ("large integer implicitly truncated
to unsigned type") on all systems that use this driver. The warning
results from passing long constants (TX_CFG, RX_CFG) into
smc911x_set_mac_csr() which is declared to accept "unsigned
character" arguments only.

Being close to a release, with nobody available to actually test the
code or the suggested fixes, it seems better to revert the patch.