kbuild: fix make -j N build

Make did say:
make[1]: warning: jobserver unavailable: using -j1.

Added '+' flag in relevant places to supress this warning.
Also removed some trailing tabs in same area spotted by Adrian Bunk <bunk@fs.tum.de>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -600,7 +600,7 @@ quiet_cmd_sysmap = SYSMAP
 # Generate System.map and verify that the content is consistent
 
 define rule_vmlinux__
-	$(if $(CONFIG_KALLSYMS),,$(call cmd,vmlinux_version))
+	$(if $(CONFIG_KALLSYMS),,+$(call cmd,vmlinux_version))
 
 	$(call cmd,vmlinux__)
 	$(Q)echo 'cmd_$@ := $(cmd_vmlinux__)' > $(@D)/.$(@F).cmd
@@ -653,9 +653,10 @@ define verify_kallsyms
 endef
 
 # Update vmlinux version before link
+# Use + in front of this rule to silent warning about make -j1
 cmd_ksym_ld = $(cmd_vmlinux__)
 define rule_ksym_ld
-	$(call cmd,vmlinux_version)
+	+$(call cmd,vmlinux_version)
 	$(call cmd,vmlinux__)
 	$(Q)echo 'cmd_$@ := $(cmd_vmlinux__)' > $(@D)/.$(@F).cmd
 endef