icE1usb fw: New ICE1USB_INTF_GET_ERRORS control request

This allows the host driver to obtain the current errors, as they would
normally be reported over the IRQ endpoint.  One important use case for
this is to obtain the initial error state when the driver starts up.

Change-Id: I6301bb23234c66afe083ceb500cff8a40813e8b6
diff --git a/firmware/ice40-riscv/icE1usb/ice1usb_proto.h b/firmware/ice40-riscv/icE1usb/ice1usb_proto.h
index d0d7304..9ac2136 100644
--- a/firmware/ice40-riscv/icE1usb/ice1usb_proto.h
+++ b/firmware/ice40-riscv/icE1usb/ice1usb_proto.h
@@ -32,6 +32,7 @@
 #define ICE1USB_INTF_GET_TX_CFG		0x03	/*!< struct ice1usb_tx_config */
 #define ICE1USB_INTF_SET_RX_CFG		0x04	/*!< struct ice1usb_rx_config */
 #define ICE1USB_INTF_GET_RX_CFG		0x05	/*!< struct ice1usb_rx_config */
+#define ICE1USB_INTF_GET_ERRORS		0x06	/*!< struct ice1usb_irq_err */
 
 //enum e1usb_intf_capability { };