Fix wrong KCM device icon for specific form factors

Summary:
The KCM did not know how different form factors should be displayed. The applet uses a functiun in "icon.js" to find out which icon to use. I have ported this over to the KCM.

Related: D24161

Test Plan:
Connect phone via Bluetooth and play music.

Now: "phone" icon appears
{F7458234}

Before: "audio-card" icon appears,
{F7458236}

Reviewers: #vdg, #plasma, ngraham, GB_2

Reviewed By: #vdg, ngraham

Subscribers: #plasma, plasma-devel, #vdg

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D24289