pinctrl: Adds slew-rate, input-enable/disable

This commit adds slew-rate and input-enable/disable support for pinconf
-generic.

CRs-Fixed: 668615
Change-Id: I2613a26f91dd0631c68e11feecf09bfee8297900
Signed-off-by: Sherman Yin <syin@broadcom.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Git-commit: 8ba3f4d00078e7a49c60c0bd6298f29402c3a0a0
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>