Can the Chip Select Pins be used as GPIO? It might be simpler to do that than adding a speciality to common code.
True, a GPIO pin could be re-purposed to serve as chip select, but that would involve a soldering iron and a steady hand as the P1/P2xxRDB boards are reference design boards sold by a lot of third party vendors (including Denx if I'm not mistaken) this would detract from the ability to just plug u-boot in and run with it.
People could also choose to bitbang the SPI on their custom hardware but again I feel that might defeat the purpose and spirit of u-boot. (Then again, I'm new so don't quote me on that).
Quick followup, I may have misunderstood that question. The SPI pins can only be re-purposed as extra data pins for the SDHC. It's not possible to use them as GPIO.