PHAL: Add service dependency to DEVTREE creation

Start the services that require DEVTREE after the
openpower-update-bios-attr-table.service since that's the one that
sets up the DEVTREE symlink. Also update the path to DEVTREE to the one
defined by the meson options.

Tested: Verified phal started after the bios attr service file, powered
on, and issued reboot at power on without any errors. Verified service
files had devtree path of:
Environment="PDBG_DTB=/media/hostfw/running/DEVTREE"

Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
Change-Id: If41f86b287b70c48d17c6f4b2af9aa0adfb81488
diff --git a/service_files/op-continue-mpreboot@.service.in b/service_files/op-continue-mpreboot@.service.in
index d391104..638bb1d 100644
--- a/service_files/op-continue-mpreboot@.service.in
+++ b/service_files/op-continue-mpreboot@.service.in
@@ -7,11 +7,12 @@
 Wants=obmc-power-on@%i.target
 After=obmc-power-on@%i.target
 After=start_host@%i.service
+After=openpower-update-bios-attr-table.service
 Conflicts=obmc-host-stop@%i.target
 ConditionPathExists=/run/openbmc/mpreboot@%i
 
 [Service]
-@ENABLE_PHAL_TRUE@Environment="PDBG_DTB=/var/lib/phosphor-software-manager/pnor/rw/DEVTREE"
+@ENABLE_PHAL_TRUE@Environment="PDBG_DTB=@CEC_DEVTREE_RW_PATH@"
 ExecStart=/bin/rm -f /run/openbmc/mpreboot@%i
 ExecStart=/usr/bin/openpower-proc-control startHostMpReboot
 Type=oneshot