kconfig: Move REGEX to Kconfig

Having this as a Kconfig allows it to be a dependent feature.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/novena_defconfig b/configs/novena_defconfig
index ba12075..e05c4dc 100644
--- a/configs/novena_defconfig
+++ b/configs/novena_defconfig
@@ -2,3 +2,4 @@
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/imx-common/spl_sd.cfg,MX6Q"
 CONFIG_ARM=y
 CONFIG_TARGET_KOSAGI_NOVENA=y
+CONFIG_REGEX=y