spl/powerpc: introduce CONFIG_SPL_INIT_MINIMAL

cpu_init_nand.c is renamed to spl_minimal.c as it is not really NAND-specific.

Signed-off-by: Scott Wood <scottwood@freescale.com>
---
v2: factor out START, and change cpu_init_nand.c to spl_minimal.c
Cc: Andy Fleming <afleming@freescale.com>
diff --git a/README b/README
index 211bad0..ca2d10f 100644
--- a/README
+++ b/README
@@ -2677,6 +2677,9 @@
 		For ARM, enable an optional function to print more information
 		about the running system.
 
+		CONFIG_SPL_INIT_MINIMAL
+		Arch init code should be built for a very small image
+
 		CONFIG_SPL_LIBCOMMON_SUPPORT
 		Support for common/libcommon.o in SPL binary