gpowerd: Use MACHINE_CONFIG_TEXTPROTO for config install

Allow recipes or machine configs to override the textproto configuration
file name installed to /etc/gpowerd/gpowerd_config.textproto via
MACHINE_CONFIG_TEXTPROTO. Defaults to ${MACHINE}.textproto.

Tested: Built gpowerd for various platforms and verified config installation.
Google-Bug-Id: 544946889
Fusion-Link: fusion2, n/a
Change-Id: Ib89f349a7b191df68d7775db21afdc814fb81567
Signed-off-by: Yolkee Huang <cweihuang@google.com>

recipes-google/s4/gpowerd_git.bb

diff --git a/recipes-google/s4/gpowerd_git.bb b/recipes-google/s4/gpowerd_git.bb
index 96703b9..36ef257 100644
--- a/recipes-google/s4/gpowerd_git.bb
+++ b/recipes-google/s4/gpowerd_git.bb
@@ -24,6 +24,8 @@
   "
 
 
+MACHINE_CONFIG_TEXTPROTO ?= "${MACHINE}.textproto"
+
 EXTRA_OEMESON="-Dversion=${DISTRO_VERSION} -Dinsecure_mode=disabled -Dloas3-validation=enabled"
 S = "${WORKDIR}/git"
 
@@ -52,7 +54,7 @@
   install -Dm 0644 ${WORKDIR}/43-gbmc-gpowerd.rules \
           ${D}${sysconfdir}/nftables/43-gbmc-gpowerd.rules
 
-  install -Dm 0644 ${WORKDIR}/${MACHINE}.textproto ${D}/etc/gpowerd/gpowerd_config.textproto
+  install -Dm 0644 ${WORKDIR}/${MACHINE_CONFIG_TEXTPROTO} ${D}/etc/gpowerd/gpowerd_config.textproto
 }