uboot-imx

i.mx6: mx6x_pins: Fix uart txd definitions

The uart txd pad can also provide the rxd function. But it does not stop its
tx role. This could be used for a half duplex serial port.

Change names to reduce confusion.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
CC: Troy Kisky <troy.kisky@boundarydevices.com>
CC: Jason Liu <jason.hui@linaro.org>
CC: Stefano Babic <sbabic@denx.de>
Acked-by: Jason Liu <jason.hui@linaro.org>