media: i2c: hi846: track the powered state

Add a powered state to the driver and track the state there.
Don't try to do any powering twice unnecessarily.

Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
2 jobs for 20211111_hi846_pm in 70 minutes and 14 seconds
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passed build:aarch64 #376219
librem5

00:21:34

passed build:deb #376220
librem5:arm64

01:10:14