Convert CONFIG_SYS_LOAD_ADDR to Kconfig

Now that we have consistent usage, migrate this symbol to Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/configs/openpiton_riscv64_defconfig b/configs/openpiton_riscv64_defconfig
index cd66db2..bae4dc1 100644
--- a/configs/openpiton_riscv64_defconfig
+++ b/configs/openpiton_riscv64_defconfig
@@ -10,6 +10,7 @@
 # CONFIG_LOCALVERSION_AUTO is not set
 CONFIG_ENV_VARS_UBOOT_CONFIG=y
 # CONFIG_EXPERT is not set
+CONFIG_SYS_LOAD_ADDR=0x87000000
 # CONFIG_LEGACY_IMAGE_FORMAT is not set
 # CONFIG_ARCH_FIXUP_FDT_MEMORY is not set
 CONFIG_SYS_PROMPT="openpiton$ "