Severe bug in Pracc code

The function  wait_for_pracc_rw() fails if Pracc bit is 0.
The variable ejtag_ctrl is loaded with the content of the
control register in the first scan.
In the second scan Pracc bit is scanned out as 0, letting
the proccesor go. The result is unpredictable.

All the strange data corruption when scanning at certain
frequencies, or the strange delays needed when entering
or leaving fasdata area are retated to this bug.

Now the code works at any scan frequency, tested up to 15000Khz
and indepently of processor speed, tested at 31.25Khz and 4/8Mhz.

Change-Id: Iedfd81d06d6af4bc738a521f720e42323025b268
Signed-off-by: Salvador Arroyo <sarroyofdez@yahoo.es>
Reviewed-on: http://openocd.zylin.com/769


Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>