create separate usermodehelper type for sysfs

Prevent files in /proc from incorrectly having sysfs_type attribute.

Rework neverallows so that ueventd has write access to all of
/sys which it needs to handle uevents.

Bug: 63147833
Test: Build. Flash angler, verify files are correctly labeled and no
    new denials are in the logs.

Change-Id: Ib94d44e78cee0e83e2ac924f1c72e611e8e73558