blackfin: convert blackfin board_f and board_r to use generic board init functions

- move blackfin specific cpu init code from blackfin board.c to cpu.c
- remove blackfin specific board init code and invoke generic board_f fron cpu init entry
- rename section name bss_vma to bss_start in order to match the generic board init code
- add a fake relocate_code function to set up the new stack only

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>

arch/blackfin/lib/sections.c

@@ -0,0 +1,11 @@
+/*
+ * U-boot - section.c
+ *
+ * Copyright (c) 2014 Analog Devices Inc.
+ *
+ * Licensed under the GPL-2 or later.
+ */
+
+char __bss_start[0] __attribute__((section(".__bss_start")));
+char __bss_end[0] __attribute__((section(".__bss_end")));
+char __init_end[0] __attribute__((section(".__init_end")));