pinctrl: mvebu: armada-{375,38x,39x}: normalize naming of PTP subnames

The subnames are purely informative, but it's nicer when they match
accross SoCs. This commit adjusts the Armada 375, Armada 38x and
Armada 39x MPP definitions so that the subnames of the PTP pins match
the ones used on Armada XP and Kirkwood.

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