linuxptp: refactor with LINUXPTP_MAKE_{ENV,OPTS} variables

Since there is quite some duplication in the variables to be passed in
the make environment and as make options between the build and install
steps, this commit introduces LINUXPTP_MAKE_ENV and LINUXPTP_MAKE_OPTS
to avoid the duplication.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/linuxptp/linuxptp.mk

@@ -10,27 +10,23 @@ LINUXPTP_SITE = git://git.code.sf.net/p/linuxptp/code
 LINUXPTP_LICENSE = GPL-2.0+
 LINUXPTP_LICENSE_FILES = COPYING
 
-define LINUXPTP_BUILD_CMDS
+LINUXPTP_MAKE_ENV = \
 	$(TARGET_MAKE_ENV) \
 	CROSS_COMPILE="$(TARGET_CROSS)" \
 	KBUILD_OUTPUT=$(STAGING_DIR) \
-	$(MAKE) \
-		prefix=/usr \
-		EXTRA_CFLAGS="$(TARGET_CFLAGS)" \
-		EXTRA_LDFLAGS="$(TARGET_LDFLAGS)" \
-		-C $(@D) all
+
+LINUXPTP_MAKE_OPTS = \
+	prefix=/usr \
+	EXTRA_CFLAGS="$(TARGET_CFLAGS)" \
+	EXTRA_LDFLAGS="$(TARGET_LDFLAGS)" \
+
+define LINUXPTP_BUILD_CMDS
+	$(LINUXPTP_MAKE_ENV) $(MAKE) $(LINUXPTP_MAKE_OPTS) -C $(@D) all
 endef
 
 define LINUXPTP_INSTALL_TARGET_CMDS
-	$(TARGET_MAKE_ENV) \
-	CROSS_COMPILE="$(TARGET_CROSS)" \
-	KBUILD_OUTPUT=$(STAGING_DIR) \
-	$(MAKE) \
-		prefix=/usr \
-		DESTDIR=$(TARGET_DIR) \
-		EXTRA_CFLAGS="$(TARGET_CFLAGS)" \
-		EXTRA_LDFLAGS="$(TARGET_LDFLAGS)" \
-		-C $(@D) install
+	$(LINUXPTP_MAKE_ENV) $(MAKE) $(LINUXPTP_MAKE_OPTS) \
+		DESTDIR=$(TARGET_DIR) -C $(@D) install
 
 	$(INSTALL) -D -m 644 $(LINUXPTP_PKGDIR)/linuxptp.cfg \
 		$(TARGET_DIR)/etc/linuxptp.cfg