pinctrl: mvebu: armada-{370,xp}: normalize ethernet txclkout pins

This commit normalizes the naming of the Ethernet txclkout pin to be
the same accross Marvell SoCs. It is worth mentioning that the DT
binding documentation of the Armada XP was wrong for MPP12: it said
the function was ge1(txd0), while it is in fact ge1(txclkout). It is
however not really a fix worth sending to stable since it does not
change the behavior, and the driver itself was correct.

Since only the subnames are changed, DT backward compatibility is not
affected.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>