sf: Clear display configs when hot pluggable display is disconnected

Display configs for external displays are stored in the framework
everytime we receive a hot plug to connect. However, since the
configs are not cleared on disconnect, framework will just assume
that the configs are valid. This does not work for use cases when
you connect/disconnect external displays with different resolutions.

e.g. 1080p to 4K and vice-versa

With this change we clear the display configs and repopulate when
we receive a hot plug to connect.

Change-Id: I2eeab186a8d8668a53390a2413b2ce5e044a1845
Acked-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>