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/cpu_init.c b/arch/powerpc/cpu/mpc83xx/cpu_init.c
index e6dcb8a..b2b259b 100644
--- a/arch/powerpc/cpu/mpc83xx/cpu_init.c
+++ b/arch/powerpc/cpu/mpc83xx/cpu_init.c
@@ -138,7 +138,7 @@
 		0;
 
 	/* Pointer is writable since we allocated a register for it */
-	gd = (gd_t *) (CONFIG_SYS_INIT_RAM_ADDR + CONFIG_SYS_GBL_DATA_OFFSET);
+	gd = (gd_t *)CONFIG_SYS_INIT_SP_ADDR;
 
 	/* global data region was cleared in start.S */