km-powerpc: define CONFIG_PRAM to protect PHRAM and PNVRAM

When u-boot initializes the RAM (early in boot) it looks for the "pram"
env variable to know which is area it cannot use. If the "pram" env variable
is not found, the default CONFIG_PRAM value is used.

This value used to be 0 (no protection at all). This patch sets it to a
value that covers PHRAM and PNVRAM that must be protected in our case.

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Reviewed-by: York Sun <yorksun@freescale.com>

include/configs/km/km-powerpc.h

@@ -59,8 +59,9 @@
 #define CONFIG_KM_PHRAM		0x100000
 /* resereved pram area at the end of memroy [hex] */
 #define CONFIG_KM_RESERVED_PRAM	0x0
-/* enable protected RAM */
-#define CONFIG_PRAM		0
+/* set the default PRAM value to at least PNVRAM + PHRAM when pram env variable
+ * is not valid yet, which is the case for when u-boot copies itself to RAM */
+#define CONFIG_PRAM		((CONFIG_KM_PNVRAM + CONFIG_KM_PHRAM)>>10)
 
 #define CONFIG_KM_CRAMFS_ADDR	0x800000
 #define CONFIG_KM_KERNEL_ADDR	0x400000	/* 3968Kbytes */