Add mModeSwitchingType to DisplayModeDirector

Add mModeSwitchingType to DisplayModeDirector which describes
the allow mode switching type for SurfaceFlinger. This value
is piped to SurfaceFlinger via allowGroupSwitching in
DesiredDisplayModeSpecs.

The value for mModeSwitchingType defaults to
SWITCHING_TYPE_WITHIN_GROUPS, which is the current beheviour in
SurfaceFlinger and it'll be later updated from user settings.

Bug: 161776333
Test: not yet
Change-Id: I851eaee7f86083d97204cf3553e728350c942dfe