configs: move CONFIG_SPL_TEXT_BASE to Kconfig

Moved CONFIG_SPL_TEXT_BASE to common/spl/Kconfig and migrate existing
values.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
[trini: Re-run migration]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/dh_imx6_defconfig b/configs/dh_imx6_defconfig
index 418ec21..deec9f6 100644
--- a/configs/dh_imx6_defconfig
+++ b/configs/dh_imx6_defconfig
@@ -18,6 +18,7 @@
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y
 CONFIG_BOUNCE_BUFFER=y
+CONFIG_SPL_TEXT_BASE=0x00908000
 CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SPL_SPI_LOAD=y
 CONFIG_SPL_WATCHDOG_SUPPORT=y