workflows: create-image: add banana pi r3 as target board

Only SD card for now.

Author: mattiaswal

.github/workflows/build-image.yml

@@ -9,6 +9,7 @@ on:
         required: true
         options:
           - raspberry-pi-4
+          - banana-pi-r3
         default: 'raspberry-pi-4'
       use_latest_release:
         description: 'Use latest release artifacts instead of workflow artifacts'
@@ -55,6 +56,10 @@ jobs:
               echo "BOOTLOADER=rpi4_boot" >> $GITHUB_ENV
               echo "TARGET=aarch64" >> $GITHUB_ENV
               ;;
+            banana-pi-r3)
+              echo "BOOTLOADER=mt7986_sd_boot" >> $GITHUB_ENV
+              echo "TARGET=aarch64" >> $GITHUB_ENV
+              ;;
             *)
               echo "Error: Unknown board ${{ inputs.board }}"
               exit 1