util: Allow installing to a build root

Modify util Makefiles to allow installing to a build root specified by
DESTDIR. Allows using the `install` target for packaging.

Change-Id: I3a31ea0fde9922731e1621dcc8f94b2c1326c93c
Signed-off-by: Tim Crawford <tcrawford@system76.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60540
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <patrick@coreboot.org>
Reviewed-by: Felix Singer <felixsinger@posteo.net>
diff --git a/util/ectool/Makefile b/util/ectool/Makefile
index 1ef74d2..8670def 100644
--- a/util/ectool/Makefile
+++ b/util/ectool/Makefile
@@ -22,7 +22,8 @@
 	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
 
 install: $(PROGRAM)
-	$(INSTALL) $(PROGRAM) $(PREFIX)/sbin
+	$(INSTALL) -d $(DESTDIR)$(PREFIX)/sbin
+	$(INSTALL) $(PROGRAM) $(DESTDIR)$(PREFIX)/sbin
 
 clean:
 	rm -f *.o $(PROGRAM) junit.xml
diff --git a/util/pmh7tool/Makefile b/util/pmh7tool/Makefile
index 9b3921a..0a2ebbe 100644
--- a/util/pmh7tool/Makefile
+++ b/util/pmh7tool/Makefile
@@ -12,7 +12,8 @@
 	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
 
 install: $(PROGRAM)
-	$(INSTALL) $(PROGRAM) $(PREFIX)/sbin
+	$(INSTALL) -d $(DESTDIR)$(PREFIX)/sbin
+	$(INSTALL) $(PROGRAM) $(DESTDIR)$(PREFIX)/sbin
 
 clean:
 	rm -f *.o $(PROGRAM)
diff --git a/util/spkmodem_recv/Makefile b/util/spkmodem_recv/Makefile
index c9659b4..92a3bfe 100644
--- a/util/spkmodem_recv/Makefile
+++ b/util/spkmodem_recv/Makefile
@@ -5,4 +5,5 @@
 spkmodem-recv:
 	$(CC) -o $@ $@.c
 install: spkmodem-recv
-	$(INSTALL) $< -t $(PREFIX)/bin/
+	$(INSTALL) -d $(DESTDIR)$(PREFIX)/bin/
+	$(INSTALL) $< -t $(DESTDIR)$(PREFIX)/bin/