[AD] set_gfx_mode() rewrite

["Eric Botcazou" <ebotcazou@xxxxxxxxxx>]

The attached patch is an attempt to (partially) rewrite the infamous
set_gfx_mode(). It builds upon the previous cleanup work (by Evert IIRC) and
factors out more duplicated code. It also aims at making it easier to follow
the flow-of-control.

The only (expected) functional change is when GFX_AUTODETECT_WINDOWED is
passed and gfx_cardw is set to a windowed driver that fails to start for
some reason. Previously gfx_card would have been read in order to find
another windowed driver; with the patch, set_gfx_mode() simply fails.

Tested under Windows.

P.S: Don't worry, I won't apply until after the 4.1.3 WIP release :-)

--
Eric Botcazou

Attachment: set_gfx_mode.zip
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