ata: sata_gemini: Retire custom pin control

I added a proper pin control driver for the Gemini SoC, so retire
this custom code and rely on the pin controller to set up the pads.

The "IOMUX" which is routing signals between the ATA and SATA
bridge inside of the chip is not about pin control and remains in
place.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Tejun Heo <tj@kernel.org>