staging: tidspbridge - rename bridge_brd_mem_map/unmap to a proper name

Now these functions only map user space addresses to dsp virtual
addresses, so now the functions have a more meaningful name.
Also now user_to_dsp_map returns the mapped address.

Signed-off-by: Fernando Guzman Lugo <x0095840@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>