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/brppt1_spi_defconfig b/configs/brppt1_spi_defconfig
index 7fe7f56..2072128 100644
--- a/configs/brppt1_spi_defconfig
+++ b/configs/brppt1_spi_defconfig
@@ -19,6 +19,7 @@
 CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_SPL_SPI_SUPPORT=y
 # CONFIG_EXPERT is not set
+CONFIG_SYS_LOAD_ADDR=0x80000000
 # CONFIG_FIT is not set
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_SPI_BOOT=y