OvmfPkg/QemuVideoDxe: list "Qemu.h" in the INF file

OvmfPkg/QemuVideoDxe: list "Qemu.h" in the INF file

Among many other things, "Qemu.h" declares the
QemuVideoGraphicsOutputConstructor() and
QemuVideoGraphicsOutputDestructor() functions, which are defined in
"Gop.c", and called from "Driver.c".

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Phil Dennis-Jordan <phil@philjordan.eu>
Suggested-by: Michael Kinney <michael.d.kinney@intel.com>
Ref: http://mid.mail-archive.com/E92EE9817A31E24EB0585FDF735412F56327F7D3@ORSMSX113.amr.corp.intel.com
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>