bootloader: disconnect VRTC from SAR input in bootloader_random_disable

Bootloader enables SAR ADC in test mode to get some entropy for the RNG.
The bits which control the ADC test mux were not disabled, which caused
extra ~24uA current to be drawn from VRTC, increasing deep sleep current
consumption. This change disables relevant test mode bits in
bootloader_random_disable.

components/bootloader_support/src/bootloader_random.c

@@ -135,4 +135,8 @@ void bootloader_random_disable(void)
     /* Reset i2s peripheral */
     SET_PERI_REG_MASK(DPORT_PERIP_RST_EN_REG, DPORT_I2S0_RST);
     CLEAR_PERI_REG_MASK(DPORT_PERIP_RST_EN_REG, DPORT_I2S0_RST);
+
+    /* Disable pull supply voltage to SAR ADC */
+    CLEAR_PERI_REG_MASK(RTC_CNTL_TEST_MUX_REG, RTC_CNTL_ENT_RTC);
+    SET_PERI_REG_BITS(RTC_CNTL_TEST_MUX_REG, RTC_CNTL_DTEST_RTC, 0, RTC_CNTL_DTEST_RTC_S);
 }