powerpc: Switch to using CONFIG_SYS_INIT_SP_OFFSET from CONFIG_SYS_GBL_DATA_OFFSET

In the places where PowerPC references CONFIG_SYS_GBL_DATA_OFFSET it
does so as (CONFIG_SYS_INIT_RAM_ADDR + CONFIG_SYS_GBL_DATA_OFFSET).  And
it defines CONFIG_SYS_GBL_DATA_OFFSET in the same manner that other
architectures define CONFIG_SYS_INIT_SP_OFFSET. Other architectures
define CONFIG_SYS_INIT_SP_ADDR as (CONFIG_SYS_INIT_RAM_ADDR +
CONFIG_SYS_INIT_SP_OFFSET) typically.  Rename things within PowerPC for
consistency with other architectures.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/powerpc/cpu/mpc83xx/start.S b/arch/powerpc/cpu/mpc83xx/start.S
index 7a01b16..b136456 100644
--- a/arch/powerpc/cpu/mpc83xx/start.S
+++ b/arch/powerpc/cpu/mpc83xx/start.S
@@ -229,8 +229,8 @@
 	/* set up the stack pointer in our newly created
 	 * cache-ram; use r3 to keep the new SP for now to
 	 * avoid overiding the SP it uselessly */
-	lis	r3, (CONFIG_SYS_INIT_RAM_ADDR + CONFIG_SYS_GBL_DATA_OFFSET)@h
-	ori	r3, r3, (CONFIG_SYS_INIT_RAM_ADDR + CONFIG_SYS_GBL_DATA_OFFSET)@l
+	lis	r3, CONFIG_SYS_INIT_SP_ADDR@h
+	ori	r3, r3, CONFIG_SYS_INIT_SP_ADDR@l
 
 	/* r4 = end of GD area */
 	addi r4, r3, GENERATED_GBL_DATA_SIZE