perf vendor events arm64: Add JSON metrics for imx8mp DDR Perf

Add JSON metrics for imx8mp DDR Perf.
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de> <s.hauer@pengutronix.de>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-imx@nxp.com
Cc: kernel@pengutronix.de
Link: https://lore.kernel.org/r/20210127105734.12198-5-qiangqing.zhang@nxp.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/pmu-events/arch/arm64/freescale/imx8mp/sys/ddrc.json

+[
+   {
+           "BriefDescription": "ddr cycles event",
+           "EventCode": "0x00",
+           "EventName": "imx8mp_ddr.cycles",
+           "Unit": "imx8_ddr",
+           "Compat": "i.MX8MP"
+   },
+   {
+           "BriefDescription": "ddr read-cycles event",
+           "EventCode": "0x2a",
+           "EventName": "imx8mp_ddr.read_cycles",
+           "Unit": "imx8_ddr",
+           "Compat": "i.MX8MP"
+   },
+   {
+           "BriefDescription": "ddr write-cycles event",
+           "EventCode": "0x2b",
+           "EventName": "imx8mp_ddr.write_cycles",
+           "Unit": "imx8_ddr",
+           "Compat": "i.MX8MP"
+   },
+   {
+           "BriefDescription": "ddr read event",
+           "EventCode": "0x35",
+           "EventName": "imx8mp_ddr.read",
+           "Unit": "imx8_ddr",
+           "Compat": "i.MX8MP"
+   },
+   {
+           "BriefDescription": "ddr write event",
+           "EventCode": "0x38",
+           "EventName": "imx8mp_ddr.write",
+           "Unit": "imx8_ddr",
+           "Compat": "i.MX8MP"
+   }
+]