staging: xgifb: remove macros with hidden variable

This patch removes macros in XGI_main.h that contain a xgifb_info
variable.  These macros hurt readability by hiding said variable
behind a define.  It also uses a temporary variable to keep the
replaced code from getting too long.

Signed-off-by: Joshua Abraham <j.abraham1776@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>