Add target_data_bits().

This is used to compute memory block read alignment, and specifically
allows 64-bit targets to ensure that memory block reads are only
requested on 64-bit boundaries.

Signed-off-by: Tim Newsome <tim@sifive.com>
Change-Id: Idb1a27b9fc02c46245556bb0f3d6d94b368c4817
Reviewed-on: http://openocd.zylin.com/6249
Reviewed-by: Marc Schink <dev@zapb.de>
Tested-by: jenkins
Reviewed-by: Jan Matyas <matyas@codasip.com>
Reviewed-by: Xiang W <wxjstz@126.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/target.h

@@ -684,6 +684,13 @@ target_addr_t target_address_max(struct target *target);
  */
 unsigned target_address_bits(struct target *target);
 
+/**
+ * Return the number of data bits this target supports.
+ *
+ * This routine is a wrapper for target->type->data_bits.
+ */
+unsigned int target_data_bits(struct target *target);
+
 /** Return the *name* of this targets current state */
 const char *target_state_name(struct target *target);