drivers: i2s: i2s_sam_ssc: Convert to devicetree

Convert i2s_sam_ssc driver to utilize devicetree.  We replace Kconfig
options for specifying the DMA configuration (channel, DMA device name)
with getting that from devicetree.  We also get pincfg from devicetree,
however we still have Kconfig sybmols to specify if the RF or RK pin is
enabled.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>