jtag_interface: .speed can be NULL when not needed

adapter_init (core.c) won't check speed configuration
of the selected interface if it's not needed (.speed = NULL).

When it's not needed, we can now omit adapter_khz in
init scripts and we don't have to implement dummy handlers
for speed_div and khz functions.

It also removes calls to adapter_khz in interface configuration
files when not used anymore.

Change-Id: I6eb1894385503fede542a368f297cec6565eed44
Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
Reviewed-on: http://openocd.zylin.com/1131
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>

tcl/interface/altera-usb-blaster.cfg

@@ -8,4 +8,3 @@ interface usb_blaster
 # These are already the defaults.
 # usb_blaster_vid_pid 0x09FB 0x6001
 # usb_blaster_device_desc "USB-Blaster"
-adapter_khz 3000

tcl/interface/osbdm.cfg

@@ -5,8 +5,3 @@
 #
 interface osbdm
 reset_config srst_only
-
-#
-# OSBDM doesn't support speed control
-#
-adapter_khz 1

tcl/interface/stlink-v1.cfg

@@ -7,5 +7,3 @@ hla_layout stlink
 hla_device_desc "ST-LINK/V1"
 hla_vid_pid 0x0483 0x3744
 
-# unused but set to disable warnings
-adapter_khz 1000

tcl/interface/stlink-v2.cfg

@@ -7,5 +7,3 @@ hla_layout stlink
 hla_device_desc "ST-LINK/V2"
 hla_vid_pid 0x0483 0x3748
 
-# unused but set to disable warnings
-adapter_khz 1000

tcl/interface/sysfsgpio-raspberrypi.cfg

@@ -10,9 +10,6 @@
 
 interface sysfsgpio
 
-# This has no effect on the driver, but is required
-adapter_khz 100
-
 # Each of the JTAG lines need a gpio number set: tck tms tdi tdo
 # Header pin numbers: 23 22 19 21
 sysfsgpio_jtag_nums 11 25 10 9

tcl/interface/ti-icdi.cfg

@@ -11,5 +11,3 @@ interface hla
 hla_layout ti-icdi
 hla_vid_pid 0x1cbe 0x00fd
 
-# unused but set to disable warnings
-adapter_khz 1000

tcl/interface/usb-jtag.cfg

@@ -7,5 +7,3 @@
 interface usb_blaster
 usb_blaster_vid_pid 0x16C0 0x06AD
 usb_blaster_device_desc "USB-JTAG-IF"
-adapter_khz 3000
-