drm/qxl: get vga ioports

qxl has two modes: "native" (used by the drm driver) and "vga" (vga
compatibility mode, typically used for boot display and firmware
framebuffers).

Accessing any vga ioport will switch the qxl device into vga mode.
The qxl driver never does that, but other drivers accessing vga ports
can trigger that too and therefore disturb qxl operation.  So aquire
the legacy vga ioports from vgaarb to avoid that.

Reproducer: Boot kvm guest with both qxl and i915 vgpu, with qxl being
first in pci scan order.

v2: Skip this for secondary qxl cards which don't have vga mode in the
    first place (Frediano).

Cc: Frediano Ziglio <fziglio@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20190805105401.29874-1-kraxel@redhat.com