Powercap: add p8 support

P8 uses i2c-occ and powercap is not created.
Add P8 support by creating powercap object with i2c device name.

Fixes openbmc/openbmc#2688

Change-Id: Ia63070d63f4392cc4b084ab628cdbdcf4206c883
Signed-off-by: Lei YU <mine260309@gmail.com>
6 files changed