phosphor-state-manager: Add reset cause logic This change will allow BMC graceful reboots to be tracked differently from crashes. Tested: busctl set-property xyz.openbmc_project.State.BMC /xyz/openbmc_project/state/bmc0 xyz.openbmc_project.State.BMC RequestedBMCTransition s xyz.openbmc_project.State.BMC.Transition.Reboot ... <bmc reboots> ... Jan 24 22:27:58 <>-nfd01.prod.google.com phosphor-bmc-state-manager[435]: Rest flag file found openbmc review for ref: https://gerrit.openbmc.org/c/openbmc/phosphor-state-manager/+/77551 Fusion-Link: https://fusion2.corp.google.com/3e6b34e0-7051-3d66-850b-35203e3520f0 Google-Bug-Id: 388883002 Change-Id: I85b415dbdbf6babb1bc262a230303d6c860450eb Signed-off-by: John Edward Broadbent <jebr@google.com>