Add support to configure multiple pins in each register, existing
implementation added by [1] does not support full fledge multiple pin
configuration in single register, reports a pin clash when different
modules configure different bits of same register. The issue reported
and discussed here
http://www.spinics.net/lists/arm-kernel/msg235213.html

With pinctrl-single,bits-per-mux property specified, use function-mask
property to find out number pins to configure. Allocate and register
pin control functions based sub mask.

Tested on da850/omap-l138 EVM.
does not support variable submask for pins.
does not support pinconf.

[1] "pinctrl: pinctrl-single: Add pinctrl-single,bits type of mux"
(9e605cb6),
Signed-off-by: Manjunathappa, Prakash <prakash.pm@ti.com>
Reported-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Tested-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>