recipes-kernel: make perf a standalone package

perf has been coupled to the kernel packages via kernel.bbclass.
While maintaining the build of perf out of the kernel source tree
is desired the package coupling has proved to be awkward in
several situations such as:

  - when a kernel recipe doesn't want to build/provide perf
  - when licensing of dependencies would prohibit perf and hence
    the kernel from being built.

To solve some of these problems, this recipe is the extraction of
the linux-tools.inc provided perf compilation into a standalone
perf recipe that builds out of the kernel source, but is otherwise
independent.

No new functionality is provided above what the linux-tools.inc
variant provided, but the separate recipe provides baseline for
adding new functionality.

Signed-off-by: Liang Li <liang.li@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>