pinctrl: mvebu: remove obsolete per-control name buffer allocation

With the introduction of a global name buffer, we can now remove
the allocation and preparation of per-control name buffers.

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