tcl: target: icepick: add icepick_d_tapenable procedure

tcl: target: icepick: add icepick_d_tapenable procedure

instead of replicating icepick_d_tapenable in many of TI's newer
platforms, we can move to icepick.cfg and just call it from board TCL
configuration file.  This is similar to the C but has a few changes we
need to make.

Change-Id: I0ab48005ccd66cd5b67b919fb5e3b462288f211d
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tom Rini <trini@ti.com>
Reviewed-on: http://openocd.zylin.com/2030
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>