thermal: tsens: Pass register offsets as private data

Registers have moved around across TSENS generations. For example, the
CTRL register was at offset 0x0 in the SROT region on msm8916 but is at
offset 0x4 in newer v2 based TSENS HW blocks.

Allow passing offsets of important registers so that we can continue to
use common functions.

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>