powerpc/85xx: introduce and document CONFIG_SYS_CCSRBAR macros

Introduce the CONFIG_SYS_CCSRBAR_PHYS_HIGH and CONFIG_SYS_CCSRBAR_PHYS_LOW
macros, which contain the high and low portions of CONFIG_SYS_CCSRBAR_PHYS.
This is necessary for the assembly-language code that relocates CCSR, since
the assembler does not understand 64-bit constants.

CONFIG_SYS_CCSRBAR_PHYS is automatically defined from the
CONFIG_SYS_CCSRBAR_PHYS_HIGH and CONFIG_SYS_CCSRBAR_PHYS_LOW macros, so it
should not be defined in a board header file.  Similarly,
CONFIG_SYS_CCSRBAR_DEFAULT is defined for each SOC in config_mpc85xx.h, so
it should also not be defined in the board header file.

CONFIG_SYS_CCSR_DO_NOT_RELOCATE is a "short-cut" macro that guarantees that
CONFIG_SYS_CCSRBAR_PHYS is set to the same value as CONFIG_SYS_CCSRBAR_DEFAULT,
and so CCSR will not be relocated.

Since CONFIG_SYS_CCSRBAR_DEFAULT is locked to a fixed value, multi-stage U-Boot
builds (e.g. NAND) are required to relocate CCSR only during the last stage
(i.e. the "real" U-Boot).  All other stages should define
CONFIG_SYS_CCSR_DO_NOT_RELOCATE to ensure that CCSR is not relocated.

README is updated with descriptions of all the CONFIG_SYS_CCSRBAR_xxx macros.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/include/configs/stxgp3.h b/include/configs/stxgp3.h
index fc3881d..66738d5 100644
--- a/include/configs/stxgp3.h
+++ b/include/configs/stxgp3.h
@@ -109,12 +109,9 @@
 
 #ifdef CONFIG_SYS_RAMBOOT
 #define CONFIG_SYS_CCSRBAR_DEFAULT	0x40000000	/* CCSRBAR by BDI cfg	*/
-#else
-#define CONFIG_SYS_CCSRBAR_DEFAULT	0xff700000	/* CCSRBAR Default	*/
 #endif
-#define CONFIG_SYS_CCSRBAR             0xfdf00000      /* relocated CCSRBAR    */
-#define CONFIG_SYS_CCSRBAR_PHYS	CONFIG_SYS_CCSRBAR	/* physical addr of CCSRBAR */
-#define CONFIG_SYS_IMMR		CONFIG_SYS_CCSRBAR	/* PQII uses CONFIG_SYS_IMMR	*/
+#define CONFIG_SYS_CCSRBAR		0xfdf00000
+#define CONFIG_SYS_CCSRBAR_PHYS_LOW	CONFIG_SYS_CCSRBAR
 
 /* DDR Setup */
 #define CONFIG_FSL_DDR1