Add GPIOLIB and OF as dependencies for PINCTRL_MSM8X74, to fix
build errors from i386-randconfig.
Also add help text and make the entries tristate, while touching
these entries.

Cc: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: NBjorn Andersson <bjorn.andersson@sonymobile.com>
[Rebased on top of pin control development branch]
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>