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/phal-import-devtree@.service.in b/service_files/phal-import-devtree@.service.in
index 08dc4c2..53bde5a 100644
--- a/service_files/phal-import-devtree@.service.in
+++ b/service_files/phal-import-devtree@.service.in
@@ -2,6 +2,7 @@
 Description=Import Host%i PHAL devtree attributes
 After=obmc-host-reset-running@%i.target
 Before=attn_handler.service
+After=openpower-update-bios-attr-table.service
 ConditionPathExists=/run/openbmc/chassis@%i-on
 ConditionPathExists=/run/openbmc/host@%i-on