sysreset: Support a hot reset

In some cases we may wish to return back to the program which started
U-Boot. Add the concept of a 'hot' reset, to support this.

Signed-off-by: Simon Glass <sjg@chromium.org>

cmd/boot.c

@@ -60,6 +60,7 @@ U_BOOT_CMD(
 	reset, 2, 0,	do_reset,
 	"Perform RESET of the CPU",
 	"- cold boot without level specifier\n"
+	"reset -h - hotreset if implemented\n"
 	"reset -w - warm reset if implemented"
 );