Support for SST 39VF3201C NOR flash

 * Add Thumb-2 code to write flash memories that don't support DQ5 polling
 * Make sure default values for unlock commands are set even if there is no PRI information given by the flash
 * Add a fixup to disable DQ5 polling for the SST 39VF3201C

Change-Id: Ib08cf20547d0f500d5f78241521e6b49050c3d40
Signed-off-by: IS2T development team <dev.is2t@gmail.com>
Reviewed-on: http://openocd.zylin.com/1449
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>