adding GM mode

Create the a new inout register to setup default value.
use it instead of GPIO register for O_E_N and TERM_E.

WR-NIC was almost out of Block RAM when sythesis was done with chipscope. Then
ISE was trying to pack descriptors' buffers in wrsw_nic into distributed RAM
instead of block RAM. As a result FSMs inside wrsw_nic were able to read
descriptors written by the linux driver, but linux driver was not able to read
updated descriptors written by FSMs. This commit fixes this problem by reducing
the amount of RAM utilized by chipscope cores.

wrsw_dio/pulse_gen_pl: removed 1-subtraction from the pulse start time, which was calculated incorrectly for timestamps with cycles value == 0. Now the subtraction is done in the NIC driver