kbuild: Fix instrumentation removal breakage on avr32

AVR32 still includes Kconfig.instrumentation, so it won't build after
this...

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>