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/at91sam9n12ek_nandflash_defconfig b/configs/at91sam9n12ek_nandflash_defconfig
index 5e727cf..65fefe1 100644
--- a/configs/at91sam9n12ek_nandflash_defconfig
+++ b/configs/at91sam9n12ek_nandflash_defconfig
@@ -1,7 +1,7 @@
 CONFIG_ARM=y
 CONFIG_SKIP_LOWLEVEL_INIT=y
 CONFIG_ARCH_AT91=y
-CONFIG_SYS_TEXT_BASE=0x26f00000
+CONFIG_TEXT_BASE=0x26f00000
 CONFIG_TARGET_AT91SAM9N12EK=y
 CONFIG_NR_DRAM_BANKS=1
 CONFIG_DM_GPIO=y