perf tools: Add the right header to obtain PERF_ALIGN()

The util/event.h header needs PERF_ALIGN(), but wasn't including
linux/kernel.h, where it is defined, instead it was getting it by
luck by including map.h, which it doesn't need at all.

Fix it by including the right header.

Link: http://lkml.kernel.org/n/tip-nf3t9blzm5ncoxsczi8oy9mx@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>