ARM: Add support for S3C6400 based SMDK6400 board

SMDK6400 can only boot U-Boot from NAND-flash. This patch adds a nand_spl
driver for it too. The board can also boot from the NOR flash, but due to
hardware limitations it can only address 64KiB on it, which is not enough
for U-Boot. Based on the original sources by Samsung for U-Boot 1.1.6.

Signed-off-by: Guennadi Liakhovetski <lg@denx.de>
diff --git a/MAINTAINERS b/MAINTAINERS
index 57a79b4..4d58fc7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -531,6 +531,7 @@
 Guennadi Liakhovetski <g.liakhovetski@gmx.de>
 
 	mx31ads		i.MX31
+	SMDK6400	S3C6400
 
 David Müller <d.mueller@elsoft.ch>