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/misc.c b/firmware/ice40-riscv/icE1usb/misc.c
index 4fdd2f5..dca126a 100644
--- a/firmware/ice40-riscv/icE1usb/misc.c
+++ b/firmware/ice40-riscv/icE1usb/misc.c
@@ -56,3 +56,9 @@
 {
 	return misc_regs->e1_tick[0].tx;
 }
+
+void
+reboot(int fw)
+{
+	misc_regs->warmboot = (1 << 2) | (fw << 0);
+}