oniro-{image,linux}: use x-gpt-efi-disk for QEMU x86

Similar to how the SECO board was handled, the QEMU x86 machine can now
use EFI and GRUB correctly. This change is split over three parts,
MACHINE_FEATURES is modified to enable efi, WKS_FILE_DEPENDS to build
EFI firmware and lastly WKS_FILE to pick the new unified kick-start
file.

This was tested with:

        qemu-system-i386 -cpu IvyBridge -machine q35 -bios ovmf.qcow2 \
                oniro-image-base-qemux86.wic -m 1024 -nographic

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>