x86/build: Clean auto-generated processor feature files

Commit 9def39be4e96 ("x86: Support compiling out human-friendly
processor feature names") made two source file targets
conditional. Such conditional targets will not be cleaned
automatically by make mrproper.

Fix by adding explicit clean-files targets for the two files.

Fixes: 9def39be4e96 ("x86: Support compiling out human-friendly processor feature names")
Signed-off-by: Bjørn Mork <[e-mail]>
Cc: Josh Triplett <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/boot/Makefile

···
 $(obj)/cpustr.h: $(obj)/mkcpustr FORCE
 	$(call if_changed,cpustr)
 endif
+clean-files += cpustr.h
 
 # ---------------------------------------------------------------------------
 

arch/x86/kernel/cpu/Makefile

···
 $(obj)/capflags.c: $(cpufeature) $(src)/mkcapflags.sh FORCE
 	$(call if_changed,mkcapflags)
 endif
+clean-files += capflags.c