aarch64: add support for "reset halt"

aarch64: add support for "reset halt"

Support halting the CPU directly after a reset. If halt is
requested, the CPU stops directly at the reset vector, before
any code is executed.

This functionality was implemented using the Reset Catch
debug event.

Change-Id: If90d54c088442340376f0b588ba10267ea8e7327
Signed-off-by: Christian Hoff <christian.hoff@advantest.com>
Reviewed-on: http://openocd.zylin.com/5947
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>