sparc: move CONFIG_SYS_TEXT_BASE to Kconfig

Defining CONFIG_SYS_TEXT_BASE in config.mk is very old style.

Create CONFIG_SYS_TEXT_BASE option in Kconfig, but let it
depend on CONFIG_SPARC because we do not want to disturb
the other architectures that still define CONFIG_SYS_TEXT_BASE
in their header files.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Daniel Hellstrom <daniel@gaisler.com>
diff --git a/configs/gr_xc3s_1500_defconfig b/configs/gr_xc3s_1500_defconfig
index da846db..fecdd25 100644
--- a/configs/gr_xc3s_1500_defconfig
+++ b/configs/gr_xc3s_1500_defconfig
@@ -1,2 +1,3 @@
+CONFIG_SYS_TEXT_BASE=0x00000000
 CONFIG_SPARC=y
 CONFIG_TARGET_GR_XC3S_1500=y