drm/panel: simple: add a macro for defining display modes in a simpler and less error...

drm/panel: simple: add a macro for defining display modes in a simpler and less error prone way

Create a macro that eases the definition of display mode parameters by
accecpting the parameters:
freq, hactive, hfront-porch, hsynclen, hback-porch,
vactive, vfront-porch, vsynclen, vback-porch, vrefresh
that can be usually directly taken from an LCD datasheet.

Put the calculations that are now open coded repeating the same
parameters multiple times into the macro expansion.