fix(soc): set ESP32-C6 DIS_DOWNLOAD_MSPI capability

ESP32-C6 has the SPI_DOWNLOAD_MSPI_DIS eFuse but lacked the capability, so
flash-encryption release mode never disabled MSPI access from download mode.

C6's WR_DIS.SPI_DOWNLOAD_MSPI_DIS (bit 17) is not shared with any other eFuse, so
already-provisioned devices can still burn it.

components/soc/esp32c6/include/soc/Kconfig.soc_caps.in

@@ -923,6 +923,10 @@ config SOC_EFUSE_DIS_ICACHE
     bool
     default y
 
+config SOC_EFUSE_DIS_DOWNLOAD_MSPI
+    bool
+    default y
+
 config SOC_EFUSE_BLOCK9_KEY_PURPOSE_QUIRK
     bool
     default y

components/soc/esp32c6/include/soc/soc_caps.h

@@ -383,6 +383,8 @@
 #define SOC_EFUSE_DIS_DIRECT_BOOT 1
 #define SOC_EFUSE_SOFT_DIS_JTAG 1
 #define SOC_EFUSE_DIS_ICACHE 1
+/* Capability to disable the MSPI access in download mode */
+#define SOC_EFUSE_DIS_DOWNLOAD_MSPI 1
 #define SOC_EFUSE_BLOCK9_KEY_PURPOSE_QUIRK 1  // XTS-AES key purpose not supported for this block
 #define SOC_EFUSE_XTS_AES_KEY_128 1