meta-phosphor: change systemd.bbclass to match upstream override syntax

Upstream bbclasses changed to typically use the `:${PN}` override
syntax, including the SYSTEMD_ variables.  Change our systemd.bbclass
to do the same for consistency and perform a tree-wide variable
replacement.

Spot checked by building bletchley and witherspoon and checking
some of the SYSTEMD_LINK directives on installed packages under qemu.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I20a9dd809bff8af8759488734f80486c7228c6eb
diff --git a/meta-phosphor/recipes-phosphor/leds/phosphor-led-manager_git.bb b/meta-phosphor/recipes-phosphor/leds/phosphor-led-manager_git.bb
index 341c5f7..3bfd47d 100644
--- a/meta-phosphor/recipes-phosphor/leds/phosphor-led-manager_git.bb
+++ b/meta-phosphor/recipes-phosphor/leds/phosphor-led-manager_git.bb
@@ -39,7 +39,7 @@
 SYSTEMD_SERVICE:${PN} += "obmc-led-group-start@.service obmc-led-group-stop@.service"
 SYSTEMD_SERVICE:${PN}-faultmonitor += "obmc-fru-fault-monitor.service"
 
-SYSTEMD_LINK_${PN} += "../obmc-led-group-start@.service:multi-user.target.wants/obmc-led-group-start@bmc_booted.service"
+SYSTEMD_LINK:${PN} += "../obmc-led-group-start@.service:multi-user.target.wants/obmc-led-group-start@bmc_booted.service"
 
 CHASSIS_TARGETS = "poweron poweroff"
 STATES = "start stop"
@@ -47,10 +47,10 @@
 TGTFMT = "obmc-chassis-{0}@0.target"
 INSTFMT = "obmc-led-group-{1}@power_on.service"
 FMT = "../${TMPLFMT}:${TGTFMT}.wants/${INSTFMT}"
-SYSTEMD_LINK_${PN} += "${@compose_list_zip(d, 'FMT', 'CHASSIS_TARGETS', 'STATES')}"
+SYSTEMD_LINK:${PN} += "${@compose_list_zip(d, 'FMT', 'CHASSIS_TARGETS', 'STATES')}"
 
 # Install the override to set up a Conflicts relation
-SYSTEMD_OVERRIDE_${PN} += "bmc_booted.conf:obmc-led-group-start@bmc_booted.service.d/bmc_booted.conf"
+SYSTEMD_OVERRIDE:${PN} += "bmc_booted.conf:obmc-led-group-start@bmc_booted.service.d/bmc_booted.conf"
 
 EXTRA_OEMESON:append = " -Dtests=disabled"