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/sama5d27_wlsom1_ek_mmc_defconfig b/configs/sama5d27_wlsom1_ek_mmc_defconfig
index 78a6ba6..6ea16c6 100644
--- a/configs/sama5d27_wlsom1_ek_mmc_defconfig
+++ b/configs/sama5d27_wlsom1_ek_mmc_defconfig
@@ -36,6 +36,8 @@
 CONFIG_MISC_INIT_R=y
 CONFIG_SPL_MAX_SIZE=0x10000
 CONFIG_SPL_BSS_MAX_SIZE=0x80000
+# CONFIG_SPL_SHARES_INIT_SP_ADDR is not set
+CONFIG_SPL_STACK=0x218000
 CONFIG_SPL_DISPLAY_PRINT=y
 # CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_USE_SECTOR is not set
 CONFIG_SPL_AT91_MCK_BYPASS=y