target/arm: Add PLD command to ARM disassembler.

target/arm: Add PLD command to ARM disassembler.

Updates the ARM disassembler to handle PLD (PreLoad Data) commands.
Previously handled by printing a TODO message. There are three forms of
the command: literal, register, and immediate. Simply decode based off
of the A1 encoding for the instructions in the ARM ARM. Also fixes mask
to handle PLDW commands.

Change-Id: I63bf97f16af254e838462c7cfac80f6c4681c556
Signed-off-by: James Marshall <jcmarsh@gwmail.gwu.edu>
Reviewed-on: http://openocd.zylin.com/4348
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>