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-openpower/recipes-phosphor/occ/openpower-occ-control_git.bb b/meta-openpower/recipes-phosphor/occ/openpower-occ-control_git.bb
index 3903ef6..4408291 100644
--- a/meta-openpower/recipes-phosphor/occ/openpower-occ-control_git.bb
+++ b/meta-openpower/recipes-phosphor/occ/openpower-occ-control_git.bb
@@ -55,8 +55,8 @@
 HOST_TGTFMT = "obmc-host-{1}@{2}.target"
 OCC_INSTFMT = "op-occ-{0}@{2}.service"
 HOST_OCC_FMT = "../${OCC_TMPL}:${HOST_TGTFMT}.wants/${OCC_INSTFMT}"
-SYSTEMD_LINK_${PN} += "${@compose_list_zip(d, 'HOST_OCC_FMT', 'OCC_ENABLE', 'HOST_START', 'OBMC_HOST_INSTANCES')}"
-SYSTEMD_LINK_${PN} += "${@compose_list_zip(d, 'HOST_OCC_FMT', 'OCC_DISABLE', 'HOST_STOP', 'OBMC_HOST_INSTANCES')}"
+SYSTEMD_LINK:${PN} += "${@compose_list_zip(d, 'HOST_OCC_FMT', 'OCC_ENABLE', 'HOST_START', 'OBMC_HOST_INSTANCES')}"
+SYSTEMD_LINK:${PN} += "${@compose_list_zip(d, 'HOST_OCC_FMT', 'OCC_DISABLE', 'HOST_STOP', 'OBMC_HOST_INSTANCES')}"
 
 # Set the occ disable service to be executed on host error
 HOST_ERROR_TARGETS = "crash timeout"
@@ -66,7 +66,7 @@
 OCC_DISABLE_INSTFMT = "op-occ-disable@{1}.service"
 HOST_ERROR_FMT = "../${OCC_DISABLE_TMPL}:${HOST_ERROR_TGTFMT}.wants/${OCC_DISABLE_INSTFMT}"
 
-SYSTEMD_LINK_${PN} += "${@compose_list(d, 'HOST_ERROR_FMT', 'HOST_ERROR_TARGETS', 'OBMC_HOST_INSTANCES')}"
+SYSTEMD_LINK:${PN} += "${@compose_list(d, 'HOST_ERROR_FMT', 'HOST_ERROR_TARGETS', 'OBMC_HOST_INSTANCES')}"
 
 S = "${WORKDIR}/git"