perf tools: Allow building perf source tarballs on non-configured tree

So that we don't require that the kernel be configured first, and as we
don't use KERNELRELEASE at all in the -src-pkg targets, we need o add a
new wildcard for targets ending in src-pkg:

On a make mrproper'ed kernel we get this without this patch:

[linux-2.6-tip]$ LANG= make perf-tarbz2-src-pkg
/bin/sh: include/config/kernel.release: No such file or directory
make: *** [include/config/kernel.release] Error 1
[acme@emilia linux-2.6-tip]$
Acked-by: Michal Marek <mmarek@suse.cz>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <20100604173552.GA875@ghostprotocols.net>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Makefile

@@ -1215,6 +1215,8 @@ distclean: mrproper
 # rpm target kept for backward compatibility
 package-dir	:= $(srctree)/scripts/package
 
+%src-pkg: FORCE
+	$(Q)$(MAKE) $(build)=$(package-dir) $@
 %pkg: include/config/kernel.release FORCE
 	$(Q)$(MAKE) $(build)=$(package-dir) $@
 rpm: include/config/kernel.release FORCE