Fix getscom on DDR4 everst system

The index values of pdbg targets are updated to match the physical
device path. So using the index value for getting the scoms shall fail.
The fapi position is still connected to the OMI index. So using the fapi
position to calculate the instance id in case of DDR4 system.

libpdbg/ocmb.c

@@ -48,7 +48,9 @@ static int sbefifo_ocmb_getscom(struct ocmb *ocmb, uint64_t addr, uint64_t *valu
 		struct sbefifo_context *sctx = sbefifo->get_sbefifo_context(sbefifo);
 		uint8_t instance_id;
 
-		instance_id = pdbg_target_index(&ocmb->target) & 0x0f;
+		uint32_t fapi_pos = 0;
+		pdbg_target_get_attribute(&ocmb->target, "ATTR_FAPI_POS", 4, 1, &fapi_pos);
+		instance_id = fapi_pos & 0x0f;
 
 		return sbefifo_hw_register_get(sctx,
 						SBEFIFO_TARGET_TYPE_OCMB,