Migrate CUSTOM_SYS_INIT_SP_ADDR to Kconfig using system-constants.h

- Make all users of CUSTOM_SYS_INIT_SP_ADDR reference SYS_INIT_SP_ADDR
- Introduce HAS_CUSTOM_SYS_INIT_SP_ADDR to allow for setting the stack
  pointer directly, otherwise we use the common calculation.
- On some platforms that were using the standard calculation but did not
  set CONFIG_SYS_INIT_RAM_SIZE / CONFIG_SYS_INIT_RAM_ADDR, set them.
- On a small number of platforms that were not subtracting
  GENERATED_GBL_DATA_SIZE do so now via the standard calculation.
- CONFIG_SYS_INIT_SP_OFFSET is now widely unused, so remove it from most
  board config header files.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/powerpc/cpu/mpc83xx/spl_minimal.c b/arch/powerpc/cpu/mpc83xx/spl_minimal.c
index 6d4655f..d8f6cfe 100644
--- a/arch/powerpc/cpu/mpc83xx/spl_minimal.c
+++ b/arch/powerpc/cpu/mpc83xx/spl_minimal.c
@@ -7,6 +7,7 @@
 #include <asm-offsets.h>
 #include <clock_legacy.h>
 #include <mpc83xx.h>
+#include <system-constants.h>
 #include <time.h>
 #include <asm/global_data.h>
 
@@ -25,7 +26,7 @@
 void cpu_init_f (volatile immap_t * im)
 {
 	/* Pointer is writable since we allocated a register for it */
-	gd = (gd_t *)CONFIG_SYS_INIT_SP_ADDR;
+	gd = (gd_t *)SYS_INIT_SP_ADDR;
 
 	/* global data region was cleared in start.S */