boards/risc-v: Add lvgl64_vector configuration for RISC-V QEMU

[terry0012]

Note: Please adhere to Contributing Guidelines.

Summary

Add new RISC-V 64-bit QEMU configuration with:

• 64-bit RISC-V (RV64) architecture support
• RISC-V Vector Extension (RVV/V-extension) enabled
• LVGL graphics framework integration
• VirtIO GPU and input device support
• NSH shell with built-in applications

This configuration enables developers to build and test LVGL graphical applications on 64-bit RISC-V targets with Vector extension support, providing a foundation for future SIMD optimization work.

Includes:

• defconfig: Complete configuration file with all necessary options
• Updated index.rst: Build and run instructions with QEMU launch command

Impact

CONFIG_LV_USE_NUTTX_MOUSE this config need to upgrade LVGL to 9.4.0 (apache/nuttx-apps#3253)

Testing

test lvgl and riscv v extension with this config

[acassis]

@terry0012 please normalize your defconfig:

Configuration/Tool: rv-virt/netnsh
2025-12-17 09:41:45
------------------------------------------------------------------------------------
  Cleaning...
HEAD detached at pull/17532/merge
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   boards/risc-v/qemu-rv/rv-virt/configs/lvgl64_vector/defconfig
``

[terry0012]

@terry0012 please normalize your defconfig:

Configuration/Tool: rv-virt/netnsh
2025-12-17 09:41:45
------------------------------------------------------------------------------------
  Cleaning...
HEAD detached at pull/17532/merge
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   boards/risc-v/qemu-rv/rv-virt/configs/lvgl64_vector/defconfig
``

Thanks.
Fixed with make savedefconfig & cp defconfig boards/risc-v/qemu-rv/rv-virt/configs/lvgl64_vector/