firmware/ice40-riscv: Create a reboot() function

instead of direct access to registers.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Change-Id: Iaee092c5ef651f0350b3f46386ed79fdbe06afcb
diff --git a/firmware/ice40-riscv/icE1usb/fw_app.c b/firmware/ice40-riscv/icE1usb/fw_app.c
index 17379b3..cb4dbb8 100644
--- a/firmware/ice40-riscv/icE1usb/fw_app.c
+++ b/firmware/ice40-riscv/icE1usb/fw_app.c
@@ -53,8 +53,7 @@
 	usb_disconnect();
 
 	/* Boot firmware */
-	volatile uint32_t *boot = (void*)(MISC_BASE);
-	*boot = (1 << 2) | (1 << 0);
+	reboot(1);
 }
 
 void