boot cfg: Allow Launching UMS from boot.

By using `BOOT_CFG_AUTOBOOT_EN` in `boot_cfg` and `EXTRA_CFG_NYX_UMS` in `extra_cfg` you can launch UMS from boot.

The `ums` variable must be populated with one of the following:

```
NYX_UMS_SD_CARD      0
NYX_UMS_EMMC_BOOT0   1
NYX_UMS_EMMC_BOOT1   2
NYX_UMS_EMMC_GPP     3
NYX_UMS_EMUMMC_BOOT0 4
NYX_UMS_EMUMMC_BOOT1 5
NYX_UMS_EMUMMC_GPP   6
```

bootloader/utils/util.h

@@ -23,6 +23,7 @@
 
 typedef enum
 {
+	NYX_CFG_UMS     = (1 << 6),
 	NYX_CFG_DUMP    = (1 << 7),
 } nyx_cfg_t;