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/ds414_defconfig b/configs/ds414_defconfig
index 6e4b95e..73907b3 100644
--- a/configs/ds414_defconfig
+++ b/configs/ds414_defconfig
@@ -23,6 +23,8 @@
 CONFIG_DEBUG_UART_CLOCK=250000000
 CONFIG_SYS_LOAD_ADDR=0x800000
 CONFIG_DEBUG_UART=y
+CONFIG_HAS_CUSTOM_SYS_INIT_SP_ADDR=y
+CONFIG_CUSTOM_SYS_INIT_SP_ADDR=0xff0000
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 ip=off initrd=0x8000040,8M root=/dev/md0 rw syno_hw_version=DS414r1 ihd_num=4 netif_num=2 flash_size=8 SataLedSpecial=1 HddHotplug=1"