Camera: Bump the preview frame spacer thread priority

The preview frame spacer thread is part of the camera
critical path and any scheduling delays could contribute
to frame drops and poor UX.
Increase the respective thread priority to avoid potential
delays during buffer IPC.

Bug: 355665306
Flag: com.android.internal.camera.flags.bump_preview_frame_space_priority
Test: Camera CTS
Change-Id: Id9501f7132e8b534244ab4042e42387038177ab5