Do not enable any disbled display when the mirroring switch is toggled

With the introduction of the new display connection dialog, a connected
dispaly is disabled until the user enables it by interacting with the
dialog. Therefore, we should not enable any disabled display when the
display mirroring switch is toggled.

Bug: 440988140
Test: manually
Flag: EXEMPT bugfix
Change-Id: I4aa35b11bdfc260cf3ff73058186528cd58ea6af