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/som-db5800-som-6867_defconfig b/configs/som-db5800-som-6867_defconfig
index d912ac7..5d401e6 100644
--- a/configs/som-db5800-som-6867_defconfig
+++ b/configs/som-db5800-som-6867_defconfig
@@ -1,5 +1,5 @@
 CONFIG_X86=y
-CONFIG_SYS_TEXT_BASE=0xFFF00000
+CONFIG_TEXT_BASE=0xFFF00000
 CONFIG_NR_DRAM_BANKS=8
 CONFIG_ENV_SIZE=0x1000
 CONFIG_ENV_OFFSET=0x6EF000