sun4m: Add Sun CG3 framebuffer initialisation function

In order to allow the user to choose the framebuffer for sparc-softmmu, add
-vga tcx and -vga cg3 options to the QEMU command line. If no option is
specified, the default TCX framebuffer is used.

Since proprietary FCode ROMs use a resolution of 1152x900, slightly relax the
validation rules to allow both displays to be initiated at the higher
resolution used by these ROMs upon request (OpenBIOS FCode ROMs default to
the normal QEMU sun4m default resolution of 1024x768).

Finally move any fprintf(stderr ...) statements in the areas affected by this
patch over to the new error_report() function.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
CC: Blue Swirl <blauwirbel@gmail.com>
CC: Anthony Liguori <aliguori@amazon.com>
CC: Peter Maydell <peter.maydell@linaro.org>
CC: Bob Breuer <breuerr@mc.net>
CC: Artyom Tarasenko <atar4qemu@gmail.com>
