mips32, drop unnecessary code in mips32_pracc.c

Struct mips32_pracc_context no more in use.
In current code cp0 reg/sel do not requires special handling.
In sync mode ctx.store_count not used, drop check.
In fasdata transfer function use mips32_pracc_read_ctrl_addr()
to reduce code.

Change-Id: Ibd4cfa5a44ebc106ed0db042f4e54a2e0b3d43cb
Signed-off-by: Salvador Arroyo <sarroyofdez@yahoo.es>
Reviewed-on: http://openocd.zylin.com/4007


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