stm32: adc-v2: pull up voltage regulator control.

L4 and F3 actually have the same bits to write in the same order, but F3 hides
the name of the deep power down bit.  Keep the like that for now, but there's a
standard API for enabling and disabling the regulator.

include/libopencm3/stm32/l4/adc.h

@@ -54,6 +54,15 @@
 #define ADC_CHANNEL_VBAT	18
 /**@}*/
 
+/* ADC_CR Values ------------------------------------------------------------*/
+
+/* DEEPPWD: Deep power down */
+#define ADC_CR_DEEPPWD		(1 << 29)
+
+/* ADVREGEN: Voltage regulator enable bit */
+#define ADC_CR_ADVREGEN		(1 << 28)
+
+
 /****************************************************************************/
 /* ADC_SMPRx ADC Sample Time Selection for Channels */
 /** @defgroup adc_sample ADC Sample Time Selection values