arm: mvebu: define and use common Armada XP UART2/3 pinctrl settings

This patch defines common Armada XP pinctrl settings for uart2 and
uart3 interfaces (uart0 and uart1 rx/tx do not rely on MPP):

 uart2: MPP42-43 as default
 uart3: MPP44-45 as default

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Arnaud Ebalard <arno@natisbad.org>
Link: https://lkml.kernel.org/r/fd51c080c7139a67ec01df8d797f1e88ce557796.1416613429.git.arno@natisbad.org


Signed-off-by: Jason Cooper <jason@lakedaemon.net>