drm/mgag200: Add support for G200 desktop cards

This patch adds support for G200 desktop cards. We can reuse the whole
memory and modesetting code. A few PCI and DAC register values have to
be updated accordingly.

The most significant change is in the PLL setup. The driver parses the
device's BIOS to retrieve clock limits and reference clocks. With no BIOS
found, safe defaults are being used.

v2:
	* copy BIOS ROM to system memory and access with regular
	  load/store; resolves potential HW limitations
	* fix some stray whitespaces

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Co-developed-by: Egbert Eich <eich@suse.com>
Signed-off-by: Egbert Eich <eich@suse.com>
Co-developed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200730102844.10995-9-tzimmermann@suse.de