Various log message cleanups.

Various log message cleanups.

Drop unneeded log messages, add some others that might be useful,
document which ones we're intentionally not emitting.

Don't log "$operation successful" type of messages in most cases,
that's too verbose; logging failures only is sufficient there.

baylibre-acme: Don't log "No such file or directory" messages during scan,
this triggers on all kinds of unrelated devices (e.g. "AMDGPU i2c bit
bus 0x91" in this case):

  sr: [...] baylibre-acme: Name for probe 1 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-0040/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 2 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-0041/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 3 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-0044/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 4 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-0045/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 5 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-0042/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 5 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-004c/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 6 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-0043/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 6 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-0049/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 7 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-0046/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 7 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-004f/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 8 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-0047/name”: No such file or directory
  sr: [...] baylibre-acme: Name for probe 8 can't be read: Failed to open file “/sys/class/i2c-adapter/i2c-1/1-004b/name”: No such file or directory