powerpc/include: Add data structures and macros for IMC trace mode

Add the macros needed for IMC (In-Memory Collection Counters) trace-mode
and data structure to hold the trace-imc record data.
Also, add the new type "OPAL_IMC_COUNTERS_TRACE" in 'opal-api.h', since
there is a new switch case added in the opal-calls for IMC.

Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
Reviewed-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>