thermal: tsens: Read raw qtimer value

Read the raw qtimer value when starting the detection run
and when we receive a completion to correlate the timer
values with the last VDD minimization. In addition fix
overwriting TSENS_DEBUG_BUS_SEL field when writing from
0 through 0xf.

Change-Id: Id79d9f6c5d60a2771bc9f03a9cec58ce472aa5d6
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>