devel: import perf from oldpackages

perf was in the oldpackages repository, but it makes more sense to have
it part of the default package set since we build it from the Linux
kernel sources.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43418 3c298f89-4303-0410-b956-a3cf2f4a3e73