tsc2301 - Move SPI data buffer to GFP_KERNEL memory

Because the dma_map_single() on ARM only flushes and invalidates
the cache-lines occupied by the transfer buffer, care should be
taken not to touch memory that share the same cache-lines before
starting the DMA transfer.

Signed-off-by: Klaus Pedersen <klaus.k.pedersen@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>