ppc4xx: Fix acadia_nand build problem

Don't include testdram() on NAND-booting target acadia_nand. This saves
a few bytes and makes the target build clean again.

Signed-off-by: Stefan Roese <sr@denx.de>

board/amcc/acadia/memory.c

@@ -117,7 +117,9 @@ long int initdram(int board_type)
 	return (CFG_MBYTES_RAM << 20);
 }
 
+#ifndef CONFIG_NAND_SPL
 int testdram(void)
 {
 	return (0);
 }
+#endif