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/mt7629_rfb_defconfig b/configs/mt7629_rfb_defconfig
index 5f301e0..3ee77f3 100644
--- a/configs/mt7629_rfb_defconfig
+++ b/configs/mt7629_rfb_defconfig
@@ -15,6 +15,8 @@
 CONFIG_SYS_LOAD_ADDR=0x42007f1c
 CONFIG_SPL_PAYLOAD="u-boot-lzma.img"
 CONFIG_BUILD_TARGET="u-boot-mtk.bin"
+CONFIG_HAS_CUSTOM_SYS_INIT_SP_ADDR=y
+CONFIG_CUSTOM_SYS_INIT_SP_ADDR=0x41fffef0
 CONFIG_SPL_IMAGE="spl/u-boot-spl-mtk.bin"
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y