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/socfpga_cyclone5_defconfig b/configs/socfpga_cyclone5_defconfig
index a67b0c1..d68e1c0 100644
--- a/configs/socfpga_cyclone5_defconfig
+++ b/configs/socfpga_cyclone5_defconfig
@@ -7,3 +7,4 @@
 CONFIG_ETH_DESIGNWARE=y
 CONFIG_NETDEVICES=y
 CONFIG_NET=y
+CONFIG_REGEX=y