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/snapper9g20_defconfig b/configs/snapper9g20_defconfig
index e4b5d92..6007b93 100644
--- a/configs/snapper9g20_defconfig
+++ b/configs/snapper9g20_defconfig
@@ -6,6 +6,7 @@
 CONFIG_NR_DRAM_BANKS=1
 CONFIG_ENV_SIZE=0x40000
 CONFIG_ENV_OFFSET=0x80000
+CONFIG_SYS_LOAD_ADDR=0x23000000
 CONFIG_FIT=y
 CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9G20"
 CONFIG_BOOTDELAY=3