OvmfPkg: QemuVideoDxe: clarify QEMU_VIDEO_MODE_DATA.ModeNumber

OvmfPkg: QemuVideoDxe: clarify QEMU_VIDEO_MODE_DATA.ModeNumber

The field name "ModeNumber" in QEMU_VIDEO_MODE_DATA is misleading -- it is
not immediately obvious whether this field carries a client-visible mode
number, in the GOP sense, or an internal, card type specific mode index.
After checking all references, rename the field to "InternalModeIndex".

Also, when filling in the card type independent QEMU_VIDEO_MODE_DATA array
from the card type specific mode array, distinguish the GOP mode number
from the internal mode index in the debug message.

This patch effects no functional changes.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15287 6f19259b-4bc3-4df7-8a09-765794883524