linux-firmware: add battmgr.jsn to ${PN}-qcom-qcm6490-audio

linux-firmware: add battmgr.jsn to ${PN}-qcom-qcm6490-audio

The battmgr.jsn file describes one of the services provided by the audio
DSP. Add it to the ${PN}-qcom-qcom6490-audio package (for the reference,
see the ${PN}-qcom-sc8280xp-lenovo-x13s-audio package, which also
incorporates corresponding battmgr.jsn file.

Fixes: 1d421fa263bc ("linux-firmware: Add qcom-qcm6490-{audio,compute} firmware packages")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>