convert Airoha release note from pdf to ascii and awk out a sections

```
pdftotext -layout source_import/V5.6.0/mcu/doc/Airoha_IoT_SDK_for_BT_Audio_Release_Notes.pdf - | LC_ALL=C tr -cd '\11\12\15\40-\176' > source_import/V5.6.0/mcu/doc/Airoha_IoT_SDK_for_BT_Audio_Release_Notes.txt
```

```
| awk '
/^2[[:space:]]+SDK Version 5.6.0.AB159x/ {p=1}
/^3[[:space:]]+SDK Version 5.6.0.AB157x/ {p=0}
p'
```