target: add support for 64bit data in mem2array and array2mem

target: add support for 64bit data in mem2array and array2mem

- Added support for reading and writing 64-bit data items
  using TCL commands "mem2array" and "array2mem". Until now,
  data items only up to 32 bits were supportd.

- Cleaned up functions target_array2mem() and
  target_mem2array(), especially data types of variables
  and variable declarations (scope).

Change-Id: Ia0ba427804f8fd8d7568f12714ab36984d6d5e24
Signed-off-by: Jan Matyas <matyas@codasip.com>
Reviewed-on: http://openocd.zylin.com/6286
Tested-by: jenkins
Reviewed-by: Marc Schink <dev@zapb.de>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>