configs: Migrate CONFIG_SYS_TEXT_BASE

On the NIOS2 and Xtensa architectures, we do not have
CONFIG_SYS_TEXT_BASE set.  This is a strict migration of the current
values into the defconfig and removing them from the headers.

I did not attempt to add more default values in and for now will leave
that to maintainers.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/evb-ast2500_defconfig b/configs/evb-ast2500_defconfig
index 75c62a9..1239336 100644
--- a/configs/evb-ast2500_defconfig
+++ b/configs/evb-ast2500_defconfig
@@ -1,5 +1,6 @@
 CONFIG_ARM=y
 CONFIG_ARCH_ASPEED=y
+CONFIG_SYS_TEXT_BASE=0x0
 CONFIG_ASPEED_AST2500=y
 CONFIG_TARGET_EVB_AST2500=y
 CONFIG_SYS_MALLOC_F_LEN=0x2000