openpower-software-manager:re-attach pnor mtd device to ubi

- Removed the ubiattach dependency from ubiremount.service,
  since it was attempting to reformat the pnor chip on every
  BMC reboot.
- Attempt to reattach the pnor mtd device to ubi only if it
  is formatted as ubi.

This approach will help preserve the systems that are not
formatted as ubi.

Resolves openbmc/openbmc#2061

Change-Id: I83698c05fd58a0f01c597583109d4009b02239a0
Signed-off-by: Saqib Khan <khansa@us.ibm.com>
2 files changed