MUX_ENET1_TXC was missing from both the EVK board
definition and the IO muxing configuration function
of the ENET1 driver. As a result, transmission does
not work (unless the muxing is set by default in some
board? -not the case with EVK). This commit adds the
configuration and adds the definition to i.MX93 EVK.
WARN: other, out-of-tree i.MX93 boards need to define
MUX_ENET1_TXC accordingly, otherwise build will break.
Signed-off-by: George Poulios <gpoulios@census-labs.com>