hwmon: (pmbus) Improve support for paged temperature sensors

Assumption so far was that PMBus devices would support TEMP2 and TEMP3 registers
only on page 0, and that only the TEMP1 register would be used/supported
on other pages.

Turns out that is not correct. UCD92xx devices support TEMP1 and TEMP2 on
page 0, and TEMP2 on other pages. So it is necessary to change the core code
such that it does not make a page based assumptions about temperature register
support.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>