[low-power-side] set `XOSC_TCXO_SHUTDOWN_EN` so xosc is powered down in hibernate

firmware/inc/hw_config/low-power-side.h

@@ -247,6 +247,7 @@
  * HF Clock
  */
 #define USE_XOSC				1
+#define XOSC_TCXO_SHUTDOWN_EN	1
 #define XOSC_FREQUENCY			16369000
 #define XOSC_GCLK_DIVIDE		2         /* ~8MHz on GCLK */
 #define OSC8M_GCLK_DIVIDE		1         /* ~8MHz on GCLK */