icE1usb fw: Expose the GPS NMEA data as a CDC ACM

Note that this is read-only. We drop all data from the host
because we can't have the host reconfigure the module ...

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Change-Id: Ieb6a653ece882c5f90ab27da1bca04c94184dc5a
diff --git a/firmware/ice40-riscv/icE1usb/Makefile b/firmware/ice40-riscv/icE1usb/Makefile
index 6725f6a..a6e9138 100644
--- a/firmware/ice40-riscv/icE1usb/Makefile
+++ b/firmware/ice40-riscv/icE1usb/Makefile
@@ -54,6 +54,7 @@
 	usb_desc_ids.h \
 	usb_dev.h \
 	usb_e1.h \
+	usb_gps.h \
 	usb_str_app.gen.h \
 	$(NULL)
 
@@ -65,6 +66,7 @@
 	usb_desc_app.c \
 	usb_dev.c \
 	usb_e1.c \
+	usb_gps.c \
 	$(NULL)