ati-vga: Implement DDC and EDID info from monitor

ati-vga: Implement DDC and EDID info from monitor

This adds DDC support to ati-vga and connects i2c-ddc to it. This
allows at least MacOS with an ATI ndrv, Linux radeonfb and MorphOS to
get monitor EDID info (although MorphOS splash screen is not displayed
and radeonfb needs additional tables from vgabios-rv100). Xorg needs
additional support from VESA vgabios, it's missing INT10 0x4F15
function (see
https://gitlab.freedesktop.org/xorg/xserver/blob/master/hw/xfree86/vbe/vbe.c)
without which no DDC is available that also prevents loading the
accelerated X driver.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-id: 046ddebb7ec8db48c4e877ee444ec1c41e385a74.1561028123.git.balaton@eik.bme.hu

ati-vga: Clarify comment

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-id: 20190620195213.C54127461AE@zero.eik.bme.hu

ati-vga: Add DDC reg names for debug

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-id: 20190621181459.2F8207462AA@zero.eik.bme.hu
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>