selftests/powerpc: Add test of L3 bank handling

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
selftests/powerpc: Add support for skipping tests

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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>