sepolicy: updating label on read_ahead_kb nodes

Removing read_ahead_kb nodes from sysfs_mmc_host
node. And adding sysfs_dm to perf hal and
init_shell files' allow list.
This change is being made inorder to address
the bugnizer 161927268 for legacy msm8937_32go platforms.

CRs-Fixed: 2826612
Change-Id: I190b9891eaf52fc4eb7d4fd73567572101ee288e