scripts/package/Makefile: rpmbuild add support of RPMOPTS

After commit 21a59991 ("scripts/package/Makefile: rpmbuild is needed
for rpm targets"), it is no longer possible to specify RPMOPTS.
For example, we can no longer able to control _topdir using the following
make command.
make RPMOPTS="--define '_topdir /home/xyz/workspace/'" binrpm-pkg

Fixes: 21a59991 ("scripts/package/Makefile: rpmbuild is needed for rpm targets")
Cc: <stable@vger.kernel.org> # 4.3+
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Michal Marek <mmarek@suse.com>

scripts/package/Makefile

@@ -52,7 +52,7 @@ rpm-pkg rpm: FORCE
 	$(call cmd,src_tar,$(KERNELPATH),kernel.spec)
 	$(CONFIG_SHELL) $(srctree)/scripts/mkversion > $(objtree)/.tmp_version
 	mv -f $(objtree)/.tmp_version $(objtree)/.version
-	rpmbuild --target $(UTS_MACHINE) -ta $(KERNELPATH).tar.gz
+	rpmbuild $(RPMOPTS) --target $(UTS_MACHINE) -ta $(KERNELPATH).tar.gz
 	rm $(KERNELPATH).tar.gz kernel.spec
 
 # binrpm-pkg
@@ -63,7 +63,7 @@ binrpm-pkg: FORCE
 	$(CONFIG_SHELL) $(srctree)/scripts/mkversion > $(objtree)/.tmp_version
 	mv -f $(objtree)/.tmp_version $(objtree)/.version
 
-	rpmbuild --define "_builddir $(objtree)" --target \
+	rpmbuild $(RPMOPTS) --define "_builddir $(objtree)" --target \
 		$(UTS_MACHINE) -bb $(objtree)/binkernel.spec
 	rm binkernel.spec