SPL: Add DMA library

Adding a DMA library to the SPL. It is used if CONFIG_SPL_DMA_SUPPORT is
defined.

Signed-off-by: Simon Schwarz <simonschwarzcor@gmail.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
diff --git a/doc/README.SPL b/doc/README.SPL
index d53ef9c..b4500fc 100644
--- a/doc/README.SPL
+++ b/doc/README.SPL
@@ -62,3 +62,4 @@
 CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o)
 CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o)
 CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/libnand.o)
+CONFIG_SPL_DMA_SUPPORT (drivers/dma/libdma.o)