perf tools: Remove all char * typecasts and use const in prototype

The (char *) for all the static strings was a fix for the
symptom and not the disease. The real issue was that the
function prototypes needed to be declared "const char *".

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <20091014194400.635935008@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>