target: am437x: use more descriptive names

target: am437x: use more descriptive names

Use more descriptive names for JRC and DAPs
so they more closely match documentation.

For example there's no Cortex A9 DAP, that's
the DebugSS DAP where Cortex A9 target sits. In
that same DAP we have have ETM, STM and both
dual-PRU subsystems.

Change-Id: I0e66ebb6299763f96606fae3e4c62e5785c804f2
Signed-off-by: Felipe Balbi <balbi@ti.com>
Reviewed-on: http://openocd.zylin.com/2620
Tested-by: jenkins
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Paul Fertser <fercerpav@gmail.com>