Improve dialog radiolist robustness in rockchip64_common.inc

## Description
Two improvements to enhance the robustness of the dialog radiolist implementation in `config/sources/families/include/rockchip64_common.inc`:

### 1. Harden radiolist: set item statuses and a default selection
Some dialog versions require an explicit on/off status. Also preselect the first item to reduce accidental "No SPI image chosen." when the user hits OK without navigating.

**Suggested changes:**
- Set explicit on/off status for radiolist items
- Add `--default-item "1"` to preselect the first option
- Applies to lines 317-322 and 333-338

### 2. Quote dd paths for safety
Quote paths to guard against whitespace and odd characters (low risk here, but cheap to harden).

**Suggested changes:**
- Quote the input and output paths in dd commands
- Applies to lines 326-327 and 341

## Reference
These improvements were identified during the review of PR #8556.

**Related PR:** https://github.com/armbian/build/pull/8556