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/lschlv2_defconfig b/configs/lschlv2_defconfig
index 1d55003..8a645a0 100644
--- a/configs/lschlv2_defconfig
+++ b/configs/lschlv2_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_LSXL=y
 CONFIG_IDENT_STRING=" LS-CHLv2"
 CONFIG_SYS_EXTRA_OPTIONS="LSCHLV2"
+CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_BOOTDELAY=3
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SYS_CONSOLE_INFO_QUIET=y