hwmon: (pmbus) Add tps40422 front-end driver

hwmon: (pmbus) Add tps40422 front-end driver

For TI power management chip TPS40422, READ_TEMPERATURE_2 command is supported on
page 1 of the chip, but the original driver(pmbus.c) only tried to detect this command
on page 0, this will lead to a result that the temperature sensor in page 1 couldn't
be detected. This change is to isolate the tps40422 driver from pmbus.c into a solo
front-end driver.

Signed-off-by: Zhu Laiwen <richard.zhu@nsn.com>
[Guenter Roeck: Dropped unnecessary license text (fixes checkpatch warning)]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>