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/configs/nsa310s_defconfig b/configs/nsa310s_defconfig
index 978570c..8b525eb 100644
--- a/configs/nsa310s_defconfig
+++ b/configs/nsa310s_defconfig
@@ -14,6 +14,8 @@
 CONFIG_DEFAULT_DEVICE_TREE="kirkwood-nsa310s"
 CONFIG_IDENT_STRING="\nZyXEL NSA310S/320S 1/2-Bay Power Media Server"
 CONFIG_SYS_LOAD_ADDR=0x800000
+CONFIG_HAS_CUSTOM_SYS_INIT_SP_ADDR=y
+CONFIG_CUSTOM_SYS_INIT_SP_ADDR=0xc8012000
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTCOMMAND=y
 CONFIG_BOOTCOMMAND="setenv bootargs ${console} ${mtdparts} ${bootargs_root}; ubi part root; ubifsmount ubi:rootfs; ubifsload 0x800000 ${kernel}; ubifsload 0x700000 ${fdt}; ubifsumount; fdt addr 0x700000; fdt resize; fdt chosen; bootz 0x800000 - 0x700000"