SF: Populate allowGroupSwitching from DM

Currently we use allowGroupSwitching only for testing. This CL
populates its value from DisplayManager so we can use user
setting to change its value.

Bug: 161776333
Test: atest libsurfaceflinger_unittest
Change-Id: I851eaee7f86083d97204cf3553e728350c942dfe
14 files changed