msm: arm: make nohlt readable

Make the debugfs node 'nohlt' readable.

It is a common use case to want to turn nohlt
on or off, but there is no way to see the current state.
Writing to nohlt increments or decrements its reference
counter, and does not absolutely set the state. By making
it readable, its current state can be checked so that
it can be determined if a write is needed to change the
state.

Change-Id: I08e327808299aef3e125f04bff8b6aad28d020cc
Signed-off-by: Neil Leeder <nleeder@codeaurora.org>