Button support for nucleo-h743zi2 board

[Peter Barada]

To bring myself up to speed on contributing to Nuttx, I'm adding button 
support to the Nucleo-h743zi2 board,  while testing on a nucleo-h753zi2 
board - same MB1364 board design as nucleo-h743zi2).

My question is whether to extend nucleo-h743zi2:nsh defconfig, or should 
I create a new nucleo-h743zi2:btnnsh defconfig.

Once I know which is preferred I'll generate a pull request...

Thanks in advance!

--
Peter Barada
peter.bar...@gmail.com