Revert "Modified chip select to use peripheral control bit instead of slave select"

This reverts commit 8223da01fc54524c38b2541f35296c04c41a3e96.
This commit was taken from a set of patches submitted to the kernel's SPI devel
mailing list by Harini Katakam from Xilinx.

The LKML thread can be found here:
http://thread.gmane.org/gmane.linux.kernel.spi.devel/17691

Signed-off-by: Harini Katakam <harinik@xilinx.com>
Signed-off-by: Joshua Lamorie <joshua.lamorie@xiphos.com>