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/pinebook-pro-rk3399_defconfig b/configs/pinebook-pro-rk3399_defconfig
index f97d5e8..0e215d9 100644
--- a/configs/pinebook-pro-rk3399_defconfig
+++ b/configs/pinebook-pro-rk3399_defconfig
@@ -11,6 +11,7 @@
 CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_SPL_SPI_SUPPORT=y
 CONFIG_DEBUG_UART=y
+CONFIG_SYS_LOAD_ADDR=0x800800
 CONFIG_BOOTDELAY=3
 CONFIG_USE_PREBOOT=y
 CONFIG_DEFAULT_FDT_FILE="rockchip/rk3399-pinebook-pro.dtb"