target-arm: Prepare cpreg writefns/readfns for EL3/SecExt

This patch changes some readfns/writefns to use raw_write
and raw_read functions, which use the fieldoffset specified
in ARMCPRegInfo instead of directly accessing the field.
This will simplify patches for EL3 & Security Extensions.

Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Fabian Aggeler <aggelerf@ethz.ch>
Message-id: 1401962428-14749-1-git-send-email-aggelerf@ethz.ch
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
