platform/x86: ISST: Update ioctl-number.txt for Intel Speed Select interface

Reserve ioctl numbers for intel Speed Select Technology interface
drivers.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Documentation/ioctl/ioctl-number.txt

@@ -348,3 +348,4 @@ Code  Seq#(hex)	Include File		Comments
 0xF6	all	LTTng			Linux Trace Toolkit Next Generation
 					<mailto:mathieu.desnoyers@efficios.com>
 0xFD	all	linux/dm-ioctl.h
+0xFE	all	linux/isst_if.h