thermal: adc-tm: Fix ADC_TM channel mapping

Correct channel mapping from VADC's io-channel nodes for
PMIC7 ADC.
Add compatible property for ADC_TM_IIO node
of type PMIC7, as it cannot use the same property as ADC_TM_IIO
node of type PMIC5, as channel numbers are computed differently.

Change-Id: Ib171e2139b1f4c83e78a5fe7a8d73345f75debf2
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>