cm: Add optional processing callback

Board code can optionally implement this callback. It's called whenever
we're waiting for the next command.

include/pb/cm.h

@@ -27,6 +27,7 @@ struct cm_config {
     int (*status)(uint8_t *buf, size_t *length);
     int (*password_auth)(const char *password, size_t length);
     int (*command)(uint32_t cmd, uint8_t *bfr, size_t bfr_length, uint8_t *rsp, size_t *rsp_size);
+    int (*process)(void);
     const struct cm_transport_ops tops;
 };
 

src/cm/cm_main.c

@@ -933,6 +933,16 @@ int cm_run(void)
 
         while (true) {
             plat_wdog_kick();
+
+            if (cfg->process) {
+                rc = cfg->process();
+
+                if (rc != PB_OK) {
+                    LOG_ERR("process (%i)", rc);
+                    goto err_out;
+                }
+            }
+
             rc = cfg->tops.complete();
 
             if (rc == PB_OK) {