This reverts commit ca9c8a1e,
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.