boards: nxp: frdm_mcxc242: Free Ram Region for USB Testing

Frees ram region on the frdm_mcxc242 to allow
usb samples to run on this platform due to the
constraint of 16KB ram space for this platform.

Signed-off-by: Emilio Benavente <emilio.benavente@nxp.com>

boards/nxp/frdm_mcxc242/Kconfig.defconfig

@@ -0,0 +1,16 @@
+#
+# Copyright 2025 NXP
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+if BOARD_FRDM_MCXC242
+
+if USB_CDC_ACM
+
+config USB_CDC_ACM_RINGBUF_SIZE
+	default 256
+
+endif #USB_CDC_ACM
+
+endif #BOARD_FRDM_MCXC242