Hal_Chibios: allow for faster INS sample times

we need higher priority on SPI and faster device loops

libraries/AP_HAL_ChibiOS/Device.cpp

@@ -72,8 +72,8 @@ void DeviceBus::bus_thread(void *arg)
         }
         // don't delay for less than 400usec, so one thread doesn't
         // completely dominate the CPU
-        if (delay < 400) {
-            delay = 400;
+        if (delay < 100) {
+            delay = 100;
         }
         hal.scheduler->delay_microseconds(delay);
     }

libraries/AP_HAL_ChibiOS/Scheduler.h

@@ -25,15 +25,24 @@
 #define APM_MAIN_PRIORITY_BOOST 180 // same as normal for now
 #define APM_MAIN_PRIORITY       180
 #define APM_TIMER_PRIORITY      178
-#define APM_SPI_PRIORITY        179
-#define APM_CAN_PRIORITY        177
-#define APM_I2C_PRIORITY        176
 #define APM_UART_PRIORITY        60
 #define APM_STORAGE_PRIORITY     59
 #define APM_IO_PRIORITY          58
 #define APM_SHELL_PRIORITY       57
 #define APM_STARTUP_PRIORITY     10
 
+#ifndef APM_SPI_PRIORITY
+#define APM_SPI_PRIORITY        181
+#endif
+
+#ifndef APM_CAN_PRIORITY
+#define APM_CAN_PRIORITY        177
+#endif
+
+#ifndef APM_I2C_PRIORITY
+#define APM_I2C_PRIORITY        176
+#endif
+
 /* how long to boost priority of the main thread for each main
    loop. This needs to be long enough for all interrupt-level drivers
    (mostly SPI drivers) to run, and for the main loop of the vehicle