target/arm: Remove usage of struct arm_jtag in ARMv7 targets

target/arm: Remove usage of struct arm_jtag in ARMv7 targets

The Cortex-A and Cortex-M keeps an arm_jtag struct around just to be
able to pass a pointer to it to one common JTAG function which anyway
only uses the TAP field.

Refactor the function to take a TAP directly, remove the legacy struct
from cortex instances and store the TAP pointer only in the DAP.

Cortex-M makes a call to arm_jtag_setup_connection() with the struct
but the function does nothing useful for a Cortex-M target so remove
the call.

Change-Id: I3b33709ef55372ef14522ed4337e9f2e817ae3ab
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/3142
Tested-by: jenkins
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>