pinctrl: samsung: Allow grouping multiple pinmux/pinconf nodes

One of remaining limitations of current pinctrl-samsung driver was
the inability to parse multiple pinmux/pinconf group nodes grouped
inside a single device tree node. It made defining groups of pins for
single purpose, but with different parameters very inconvenient.

This patch implements Tegra-like support for grouping multiple pinctrl
groups inside one device tree node, by completely changing the way
pin groups and functions are parsed from device tree. The code creating
pinctrl maps from DT nodes has been borrowed from pinctrl-tegra, while
the initial creation of groups and functions has been completely
rewritten with following assumptions:
 - each group consists of just one pin and does not depend on data
   from device tree,
 - each function is represented by a device tree child node of the
   pin controller, which in turn can contain multiple child nodes
   for pins that need to have different configuration values.

Device Tree bindings are fully backwards compatible. New functionality
can be used by defining a new pinctrl group consisting of several child
nodes, as on following example:

	sd4_bus8: sd4-bus-width8 {
		part-1 {
			samsung,pins = "gpk0-3", "gpk0-4",
					"gpk0-5", "gpk0-6";
			samsung,pin-function = <3>;
			samsung,pin-pud = <3>;
			samsung,pin-drv = <3>;
		};
		part-2 {
			samsung,pins = "gpk1-3", "gpk1-4",
					"gpk1-5", "gpk1-6";
			samsung,pin-function = <4>;
			samsung,pin-pud = <4>;
			samsung,pin-drv = <3>;
		};
	};

Tested on Exynos4210-Trats board and a custom Exynos4212-based one.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Cc: devicetree@vger.kernel.org
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>