graphics: nx_openwindow() and nxtk_openwindow() now accept an addtional 'flag' parameter. This argument is not used at present but will, eventually enable a RAM backed, per-window framebuffer.
graphics/Kconfig: Add configuration to support a rambacked framebuffer. Current marked as EXPERIMENTAL because this is a work in progress.
Squashed commit of the following:
graphics/: Rename nxfe_reportposition to nxmu_reportposition. The is no longer an nxfe layer.
graphics/: Renmae nxfe_redrawreq to nxmu_redrawreq. The is no longer an nxfe layer.
graphics/nxmu/nxmu.h: Renmae nxfe.h to nxmu.h. There is no long an nxfe layer.
graphics/: Rename nxfe_state_s to nxmu_state_s. There is no longer an nxfe layer.
graphics/: Rename nxfe_conn_s to nxmu_conn_s. There is no longer an nxfe layer.
