perf: Fix config file conflict with 4.1 kernels

perf: Fix config file conflict with 4.1 kernels

If you setup mutlitlibs and then:

bitbake perf libb32-perf
bitbake perf libb32-perf -c cleansstate
bitbake perf libb32-perf

you will see races where the two builds get confused about which directory
they should be using and they corrupt each other.

The issue is that .config-detected is created in ${S}, not $(OUTPUT).
We can fix this by moving the file to $(OUTPUT).

[YCOTO #8043]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>