Convert CONFIG_SPL_STACK to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_STACK

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/socfpga_stratix10_defconfig b/configs/socfpga_stratix10_defconfig
index 23050c7..a90e404 100644
--- a/configs/socfpga_stratix10_defconfig
+++ b/configs/socfpga_stratix10_defconfig
@@ -28,6 +28,8 @@
 CONFIG_BOOTCOMMAND="run fatscript; run mmcload; run linux_qspi_enable; run mmcboot"
 CONFIG_SPL_MAX_SIZE=0x40000
 CONFIG_SPL_BSS_MAX_SIZE=0x100000
+# CONFIG_SPL_SHARES_INIT_SP_ADDR is not set
+CONFIG_SPL_STACK=0xffe3f000
 CONFIG_SPL_SPI_LOAD=y
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x3C00000
 CONFIG_HUSH_PARSER=y