Rename CONFIG_SYS_TEXT_BASE to CONFIG_TEXT_BASE

The current name is inconsistent with SPL which uses CONFIG_SPL_TEXT_BASE
and this makes it imposible to use CONFIG_VAL().

Rename it to resolve this problem.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/at91sam9263ek_nandflash_defconfig b/configs/at91sam9263ek_nandflash_defconfig
index 26f3932..7714a06 100644
--- a/configs/at91sam9263ek_nandflash_defconfig
+++ b/configs/at91sam9263ek_nandflash_defconfig
@@ -2,7 +2,7 @@
 CONFIG_SKIP_LOWLEVEL_INIT=y
 CONFIG_ARCH_CPU_INIT=y
 CONFIG_ARCH_AT91=y
-CONFIG_SYS_TEXT_BASE=0x21F00000
+CONFIG_TEXT_BASE=0x21F00000
 CONFIG_SYS_MALLOC_LEN=0x80000
 CONFIG_TARGET_AT91SAM9263EK=y
 CONFIG_ATMEL_LEGACY=y