generic, x86: add tests for prctl PR_GET_TSC and PR_SET_TSC

This patch adds three tests that test whether the PR_GET_TSC and
PR_SET_TSC commands have the desirable effect.

The tests check whether the control register is updated correctly
at context switches and try to discover bugs while enabling/disabling
the timestamp counter.

Signed-off-by: Erik Bosman <ejbosman@cs.vu.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>