mips: m4k alternate pracc code. Patch 2

Each pracc function defines a variable ctx of type struct pracc_queue_info.
To simplify the code tree auxiliary functions are defined: pracc_queue_init(), pracc_add() and
pracc_queue_free().
The second parameter in pracc_add() is the store address if the instruction is a store at dmseg,
otherwise it should be 0.
The code is executed by mips32_pracc_queue_exec(). If ejtag_info->mode is 0 mips32_pracc_exec()
is called and it should work like with current code.
To generate the delay between scans the number of clock ticks are calculated with the help of
jtag_get_speed_khz(). Due to delays in the execution of each single ftdi instruction the number of ticks
are higher as it should be, specially at higher scan rates.
mips32_pracc_read_u32() should now work with the new code.

Change-Id: I471590a4fc89b56af10bd46c48767b4c64de154f
Signed-off-by: Salvador Arroyo <sarroyofdez@yahoo.es>
Reviewed-on: http://openocd.zylin.com/1194


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