meta-phosphor: disable phosphor-dbus-monitor by default

phosphor-dbus-monitor still uses autoconf and has a hard dependency on
phosphor-snmp, causing phosphor-snmp to be brought in on systems that
have no interest in using SNMP.  The vast majority of systems do not
supply any config for phosphor-dbus-monitor, so the usage of it does not
seem wide enough to enable the IMAGE_FEATURE by default.

- Remove 'obmc-dbus-monitor' from IMAGE_FEATURE by default.
- Clean up all systems that manually remove the dbus-monitor feature or
  package.
- Explicitly add the 'obmc-dbus-monitor' to the following systems:
    - meta-ibm: all
    - meta-inspur: fp5280g2
    - meta-quanta: s6q

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Iad6c4104466e21d1b9843dac964a634019eb6935