Cortex-A/R: Add missing timeout for loop polling DSCR & fix timeout types

Change-Id: I345658cfdc8a34a98418727423ac6bd562e980f3
Signed-off-by: Evan Hunter <ehunter@broadcom.com>
Reviewed-on: http://openocd.zylin.com/3201


Tested-by: jenkins
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>