common/board_f: Initialized global data for generic board

Some platforms (tested on mpc85xx, mpc86xx) use global data before calling
function baord_inti_f(). The data should not be cleared later. Any arch
which uses global data in generic board board_init_f() should define
CONFIG_SYS_GENERIC_GLOBAL_DATA.

Signed-off-by: York Sun <yorksun@freescale.com>
CC: Scott Wood <scottwood@freescale.com>
CC: Simon Glass <sjg@chromium.org>
CC: Albert ARIBAUD <albert.u.boot@aribaud.net>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/README b/README
index 61c2cac..5f89552 100644
--- a/README
+++ b/README
@@ -451,6 +451,12 @@
 		supported, core will start to execute uboot when wakes up.
 
 - Generic CPU options:
+		CONFIG_SYS_GENERIC_GLOBAL_DATA
+		Defines global data is initialized in generic board board_init_f().
+		If this macro is defined, global data is created and cleared in
+		generic board board_init_f(). Without this macro, architecture/board
+		should initialize global data before calling board_init_f().
+
 		CONFIG_SYS_BIG_ENDIAN, CONFIG_SYS_LITTLE_ENDIAN
 
 		Defines the endianess of the CPU. Implementation of those