AP_Terrain: use millis/micros/panic functions

libraries/AP_Terrain/AP_Terrain.cpp

@@ -357,7 +357,7 @@ void AP_Terrain::log_terrain_data(DataFlash_Class &dataflash)
 
     struct log_TERRAIN pkt = {
         LOG_PACKET_HEADER_INIT(LOG_TERRAIN_MSG),
-        time_us        : hal.scheduler->micros64(),
+        time_us        : AP_HAL::micros64(),
         status         : (uint8_t)status(),
         lat            : loc.lat,
         lng            : loc.lng,

libraries/AP_Terrain/TerrainGCS.cpp

@@ -64,7 +64,7 @@ bool AP_Terrain::request_missing(mavlink_channel_t chan, struct grid_cache &gcac
       ask the GCS to send a set of 4x4 grids
      */
     mavlink_msg_terrain_request_send(chan, grid.lat, grid.lon, grid_spacing, bitmap_mask & ~grid.bitmap);
-    last_request_time_ms[chan] = hal.scheduler->millis();
+    last_request_time_ms[chan] = AP_HAL::millis();
 
     return true;
 }
@@ -102,7 +102,7 @@ void AP_Terrain::send_request(mavlink_channel_t chan)
     send_terrain_report(chan, loc, true);
 
     // did we request recently?
-    if (hal.scheduler->millis() - last_request_time_ms[chan] < 2000) {
+    if (AP_HAL::millis() - last_request_time_ms[chan] < 2000) {
         // too soon to request again
         return;
     }

libraries/AP_Terrain/TerrainIO.cpp

@@ -97,7 +97,7 @@ void AP_Terrain::schedule_disk_io(void)
                 cache[cache_idx].grid = disk_block.block;
             }
             cache[cache_idx].state = GRID_CACHE_VALID;
-            cache[cache_idx].last_access_ms = hal.scheduler->millis();
+            cache[cache_idx].last_access_ms = AP_HAL::millis();
         }
         disk_io_state = DiskIoIdle;
         break;

libraries/AP_Terrain/TerrainUtil.cpp

@@ -124,7 +124,7 @@ AP_Terrain::grid_cache &AP_Terrain::find_grid_cache(const struct grid_info &info
         if (cache[i].grid.lat == info.grid_lat && 
             cache[i].grid.lon == info.grid_lon &&
             cache[i].grid.spacing == grid_spacing) {
-            cache[i].last_access_ms = hal.scheduler->millis();
+            cache[i].last_access_ms = AP_HAL::millis();
             return cache[i];
         }
         if (cache[i].last_access_ms < cache[oldest_i].last_access_ms) {
@@ -145,7 +145,7 @@ AP_Terrain::grid_cache &AP_Terrain::find_grid_cache(const struct grid_info &info
     grid.grid.lat_degrees = info.lat_degrees;
     grid.grid.lon_degrees = info.lon_degrees;
     grid.grid.version = TERRAIN_GRID_FORMAT_VERSION;
-    grid.last_access_ms = hal.scheduler->millis();
+    grid.last_access_ms = AP_HAL::millis();
 
     // mark as waiting for disk read
     grid.state = GRID_CACHE_DISKWAIT;