spi: clps711x: Convert to use CS GPIO descriptors

This converts the CLPS711x SPI master driver to use GPIO
descriptors for chip select handling.

The CLPS711x driver was merely requesting the GPIO and
setting the CS line non-asserted so this was a pretty
straight-forward conversion. The setup callback goes away.

Cc: Alexander Shiyan <shc_work@mail.ru>
Cc: Linuxarm <linuxarm@huawei.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>