techpack: Fix uapi headers_install

Since commit <d5470d14431e9d39e> ("kbuild: re-implement
Makefile.headersinst without recursion"), the headers_install
excludes Kbuild from providing information regarding uapi headers.
In fact, it recursively pulls all the headers from a given path,
in this case techpack/*. This isn't correct as techpack/ may have
non-uapi headers as well, which shouldn't be considered. Hence,
strictly look for include/uapi/$dir directory for the uapi headers.

Change-Id: Ic7b3f927bc962729da1b87ed90e5f50a1e4cd5c5
Signed-off-by: Raghavendra Rao Ananta <[email protected]>

Makefile

@@ -1356,10 +1356,10 @@ headers: $(version_h) scripts_unifdef uapi-asm-generic archheaders archscripts
 		$(MAKE) $(hdr-inst)=$$d/include/uapi; \
 	done
 
-# Deprecated. It is no-op now.
 PHONY += headers_check
-headers_check:
-	@:
+headers_check: headers
+	$(Q)$(MAKE) $(hdr-inst)=include/uapi HDRCHECK=1
+	$(Q)$(MAKE) $(hdr-inst)=arch/$(SRCARCH)/include/uapi HDRCHECK=1
 	$(Q)for d in $(techpack-dirs); do \
 		$(MAKE) $(hdr-inst)=$$d/include/uapi HDRCHECK=1; \
 	done