selftests/powerpc: Add tests of PMU EBBs

The Power8 Performance Monitor Unit (PMU) has a new feature called Event
Based Branches (EBB). This commit adds tests of the kernel API for using
EBBs.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
selftests/powerpc: Add configurable timeout to the test harness

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
selftests/powerpc: Factor out counting logic

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
selftests/powerpc: Count instructions under scheduler pressure

Have a task eat some cpu while we are counting instructions to create some
scheduler pressure. The idea being to try and unearth any bugs we have in
counting that only appear when context switching is happening.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
selftests/powerpc: Count more instructions

Although we expect some small discrepancies for very large counts, we
seem to be able to count up to 64G instructions without too much skew, so
do so.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Add stat vs record
Add BHRB tests
Add EBB BHRB tests
Add non-working EBB tests
Add fabfile