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-ampere/meta-jade/recipes-phosphor/gpio/psu-hotswap-reset.bb b/meta-ampere/meta-jade/recipes-phosphor/gpio/psu-hotswap-reset.bb
index 2ca18a0..839c6d4 100644
--- a/meta-ampere/meta-jade/recipes-phosphor/gpio/psu-hotswap-reset.bb
+++ b/meta-ampere/meta-jade/recipes-phosphor/gpio/psu-hotswap-reset.bb
@@ -13,7 +13,7 @@
 
 # Copies config file having arguments for psu
 # via GPIO assertion
-SYSTEMD_ENVIRONMENT_FILE_${PN} +="obmc/gpio/PSU1_B25 \
+SYSTEMD_ENVIRONMENT_FILE:${PN} +="obmc/gpio/PSU1_B25 \
                                   obmc/gpio/PSU2_B25 \
                                  "
 SYSTEMD_SERVICE:${PN} ?= "psu1_hotswap_reset.service psu2_hotswap_reset.service"
@@ -29,4 +29,4 @@
 GPIO_MONITOR_TGTFMT = "phosphor-gpio-monitor@{0}.service"
 TGT = "multi-user.target"
 PSU_MONITOR_FMT = "../${GPIO_MONITOR_TMPL}:${TGT}.requires/${GPIO_MONITOR_TGTFMT}"
-SYSTEMD_LINK_${PN} += "${@compose_list(d, 'PSU_MONITOR_FMT', 'OBMC_PSU_MONITOR_INSTANCES', 'OBMC_HOST_INSTANCES')}"
+SYSTEMD_LINK:${PN} += "${@compose_list(d, 'PSU_MONITOR_FMT', 'OBMC_PSU_MONITOR_INSTANCES', 'OBMC_HOST_INSTANCES')}"