EventHub: Process sysfs node changes from InputReader thread

Before syfs node change notifications were processed by EventHub, all
device openings and closings happened on the InputReader thread. The
upper layer (InputReader) makes assumptions about EventHub Device states
being synchronized with the notications of device additions and removals
from EventHub to InputReader.

The addition of sysfs node change processing moved some device openings
and closings off of the InputReader thread, which can break the
synchronization assumptions in InputReader.

In this CL, we move sysfs node change processing to the InputReader
thread.

Bug: 397208968
Bug: 358694799
Test: Presubmit
Flag: EXEMPT bug fix
Change-Id: If6d70a12ddf74098c74b8360d31c4967ae6b3d03