Allow individual devices to disable cameraserver.

cameraserver takes ~3 MiB of RAM; on some devices this is a significant
amount. Dropping the cameraserver package for these devices (which
provides cameraserver.rc) is an easy and clean way of ensuring
cameraserver doesn't start for these devices.

Bug: 118369095
Test: built image, `grep cameraserver out/target/product/$PRODUCT/installed-files.txt` shows cameraserver and cameraserver.rc
Change-Id: I23c10efbdcebca02b7a72bb77018df17e732bf2c