drivers: thermal: virtual-sensor: Add virtual sensor

Add snapshot of virtual sensor driver from kernel 4.9
as of 'commit <4291fee61276> ("drivers: qti-virtual-sensor: Add deca cpu
max virtual sensor for msm8953")'.

Change-Id: I4db7ded85cc4f3123b50e48690e0b6a0644cb91e
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>