Convert CONFIG_ENV_IS_IN_SPI_FLASH to Kconfig

This converts the following to Kconfig:
   CONFIG_ENV_IS_IN_SPI_FLASH

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/galileo_defconfig b/configs/galileo_defconfig
index f60abc3..6da437c 100644
--- a/configs/galileo_defconfig
+++ b/configs/galileo_defconfig
@@ -9,6 +9,7 @@
 CONFIG_FIT=y
 CONFIG_BOOTSTAGE=y
 CONFIG_BOOTSTAGE_REPORT=y
+CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_CONSOLE_MUX=y
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_ARCH_MISC_INIT=y