Disable low speed SPI controller

On Optimus and Sideswipe, the low speed SPI controller is not connected
except on some very early boards. Also, its FIFO is only 8 words deep.
(The high speed SPI controller has a 32-word FIFO).

Change-Id: I0d9f8d605dd8398349f0ed10b42ee7d60e0c6724
1 file changed