Add rather than override PSOC 6 macros

Use "macros_add" rather than "marcos" so any macros defined by
MCU_PSOC6 are not overwritten.

Author: c1728p9

targets/targets.json

@@ -7595,12 +7595,12 @@
     "MCU_PSOC6_M0": {
         "inherits": ["MCU_PSOC6"],
         "core": "Cortex-M0+",
-        "macros": ["MCU_PSOC6_M0"],
+        "macros_add": ["MCU_PSOC6_M0"],
         "public": false
     },
     "MCU_PSOC6_M4": {
         "inherits": ["MCU_PSOC6"],
-        "macros": ["MCU_PSOC6_M4"],
+        "macros_add": ["MCU_PSOC6_M4"],
         "public": false
     },
     "FUTURE_SEQUANA_M0": {