Add phenotype property for enabling / disabling camera pinning

Add a phenotype under runtime_native_boot for toggling camera
pinning. This will enable doing PH experiments where we disable
pinning and enable prefetching.

Bug: 141377208
Test: adb shell device_config put runtime_native_boot pin_camera false
Test: look at camera showmap

Change-Id: Ifdfcdb8e0f99e8eaf0e92c7d5a86e8d4410bae71