pinctrl: actions: Fix Kconfig dependency and help text

pinctrl: actions: Fix Kconfig dependency and help text

1. Fix Kconfig dependency for Actions Semi S900 pinctrl driver which
generates below warning in x86:

WARNING: unmet direct dependencies detected for PINCTRL_OWL
  Depends on [n]: PINCTRL [=y] && (ARCH_ACTIONS || COMPILE_TEST [=n]) && OF [=n]
  Selected by [y]:
  - PINCTRL_S900 [=y] && PINCTRL [=y]

2. Add help text for OWL pinctrl driver

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>