pinctrl: berlin: add the core pinctrl driver for Marvell Berlin SoCs

The Marvell Berlin boards have a group based pinmuxing mechanism. This
adds the core driver support. We actually do not need any information
about the pins here and only have the definition of the groups.

Let's take the example of the uart0 pinmuxing on the BG2Q. Balls BK4 and
BH6 are muxed to respectively UART0 RX and TX if the group GSM12 is set
to mode 0:

Group	Modes	Offset Base	Offset	LSB	Bit Width
GSM12	3	sm_base		0x40	0x10	0x2

Ball	Group	Mode 0		Mode 1		Mode 2
BK4	GSM12	UART0_RX	IrDA0_RX	GPIO9
BH6	GSM12	UART0_TX	IrDA0_TX	GPIO10

So in order to configure BK4 -> UART0_TX and BH6 -> UART0_RX, we need
to set (sm_base + 0x40 + 0x10) &= ff3fffff.

As pin control registers are part of either chip control or system
control registers, that deal with a bunch of other functions we rely
on a regmap instead of exclusively remapping any resources.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>