Add ResolveRootBus and IsRootBusInhibited to HwmonSysfs, implemented by
I2cSysfs. IXcHwmonBasedSensor uses them to report a bus inhibit reason, so
HwmonBasedSensor::RefreshOnceAsync skips sysfs I/O and reports STATUS_STALE
while mfgd holds an inhibit file for the root I2C bus.

Google-Bug-Id:566321613
PiperOrigin-RevId: 994150372
Change-Id: If8b73a706406e834ded1c5306dfb434d07542670