board_f: Rename initdram() to dram_init()

This allows us to use the same DRAM init function on all archs. Add a
dummy function for arc, which does not use DRAM init here.

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Dummy function on nios2]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/doc/README.mpc85xx b/doc/README.mpc85xx
index f9b023f..93ed641 100644
--- a/doc/README.mpc85xx
+++ b/doc/README.mpc85xx
@@ -156,7 +156,7 @@
        Disable	  : 15, 14
 
    11) Create DDR's TLB entriy
-       Location	  : Board_init_f -> init_func_ram -> initdram
+       Location	  : Board_init_f -> dram_init
        TLB entry  : Search free TLB entry
 
    12) Update Flash's TLB entry