Can not detect external microphone with sof sound driver

[Erin Chen]

[Summary]
Can not detect external microphone plug-in

[Steps to reproduce]
1) install BTO and boot into OS
2) test external microphone with plainbox

[Expected result]
plainbox should detect external microphone

[Actual result]
Plainbox can NOT detect external micophone plug-in

[Failure rate]
3/3
[Additional information]
SKU: NBV5-DVT2.1-C1
Image: somerville-bionic-amd64-iso-hybrid-20190418-59
Manifest: canonical-oem-somerville-bionic-amd64-20190418-59+nebula-n7-v7+X13
system-manufacturer: Dell Inc.
system-product-name: Inspiron 7590
bios-version: 1.2.0
CPU: Intel(R) Core(TM) i5-9300H CPU @ 2.40GHz (8x)
GPU: 00:02.0 VGA compatible controller [0300]: Intel Corporation Device [8086:3e9b]
kernel-version: 5.0.0-1014-oem-osp1

[Erin Chen (iamerin-c)]

Automatically attached

[Erin Chen (iamerin-c)]

Automatically attached

[Erin Chen (iamerin-c)]

Automatically attached

[Sylvain Pineau (sylvain-pineau)]

I need to following data to start debugging the problem:

- Output of `pactl list sources` before the mic plug-in
- Output of `pactl list sources` after the mic plug-in
- Output of `pactl subscribe` during the plug-in (and for 30s after the operation, to capture all events)

[Ray Chen (ray.chen)]

Verified on 201906-27088 I can not reproduced this issue

Checkbox result:https://certification.canonical.com/hardware/201906-27088/submission/153808/test/6/result/11639733/