serial: Migrate CONFIG_FSL_LINFLEXUART to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/s32v234evb_defconfig b/configs/s32v234evb_defconfig
index c59abe1..f64ed85 100644
--- a/configs/s32v234evb_defconfig
+++ b/configs/s32v234evb_defconfig
@@ -12,4 +12,5 @@
 CONFIG_DM=y
 CONFIG_FSL_ESDHC=y
 CONFIG_DM_SERIAL=y
+CONFIG_FSL_LINFLEXUART=y
 CONFIG_OF_LIBFDT=y