arm946e: don't use global variables for context

arm946e: don't use global variables for context

Global variables 'dc' 'ic' had been used in the code
to keep target's state of D-cache and I-cache
on debug entry.

This may lead to incorrect operation in configurations
with multiple cores and unequal cache states.

Fix: move cache state to the appropriate bits of the
'cp15_control_reg' field (already present but unused).
Vaule of cp15 control register stored here on
arm946e_post_debug_entry(), and analyzed later
in arm946e_write_memory().

Change-Id: I71ef82be00c21d6fffb3726cec4974d1ece70dfe
Signed-off-by: Alexander Osipenko <sipych@gmail.com>
Reviewed-on: http://openocd.zylin.com/692
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>