thermal: tsens8960: Add api to read max supported sensors

Provide api to report the maximum number of TSENS sensors
supported. Backport this from the 8974 TSENS driver
to support thermal monitor driver compilation.

Change-Id: I712ccd8169eb3df0f1e83189aea1dd98180c3e7d
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>