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/flea3_defconfig b/configs/flea3_defconfig
index 61d77eb..631dd3e 100644
--- a/configs/flea3_defconfig
+++ b/configs/flea3_defconfig
@@ -8,6 +8,7 @@
 CONFIG_SYS_I2C_MXC_I2C1=y
 CONFIG_SYS_I2C_MXC_I2C2=y
 CONFIG_SYS_I2C_MXC_I2C3=y
+CONFIG_SYS_LOAD_ADDR=0x80800000
 CONFIG_FIT=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_BOOTDELAY=3