ARM: dts: Enable Gemini flash access

Some Gemini platforms have a parallel NOR flash which conflicts
with use cases reusing some of the flash lines (such as CE1)
for GPIO.

Fix this on the D-Link DIR-685 and Itian SQ201 by creating
"enabled" and "disabled" states for the flash pin control
handle, and rely on the flash handling code to switch this
in and out when accessed so these lines can be used
for GPIO when flash is not accessed, and enable flash
access.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>