gpio: Handle deferred probing in of_find_gpio() properly

of_get_named_gpiod_flags() used directly in of_find_gpio() or indirectly
through of_find_spi_gpio() or of_find_regulator_gpio() can return
-EPROBE_DEFER. This gets overwritten by the subsequent of_find_*_gpio()
calls.

This patch fixes this by trying of_find_spi_gpio() or
of_find_regulator_gpio() only if deferred probing was not requested by
the previous of_get_named_gpiod_flags() call.

Fixes: 6a537d48 ("gpio: of: Support regulator nonstandard GPIO properties")
Fixes: c8582339 ("gpio: of: Support SPI nonstandard GPIO properties")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
[Augmented to fit with Maxime's patch]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>