pinctrl: mvebu: move resource allocation to SoC specific drivers

The way that mvebu pinctrl is designed, requesting mpp registers
in common pinctrl driver does not allow SoC specific drivers to
access this resource.

Move resource allocation in each SoC pinctrl driver and enable
already provided mpp_{set,get} callbacks.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>