runqemu: don't use qemu -vga vmware when using OVMF BIOS

The OVMF BIOS seems to prefer the defautl Cirrus emulated VGA adaptor,
otherwise the QEMU window just shows a blank screen.

NOTE: OVMF is detected simply by looking for the substring "ovmf" in the
biosdir argument to runqemu. This is, of course, not a robust test, but it
works well enough if you're just using the ovmf recipe in meta-luv.

Signed-off-by: Max Eliaser <max.eliaser@intel.com>
meta-luv: ovmf: only permit x86 and x86_64 target architectures for OVMF

While EDK2 has many components that support ARM, OVMF is not one of them. This
should be reflected in the BitBake recipe for OVMF.

This is accomplished by adding a COMPATIBLE_HOST annotation to ovmf_git.bb.

Signed-off-by: Max Eliaser <max.eliaser@intel.com>
meta-luv: ovmf: generate 32-bit firmware images when appropriate

This fixes an issue where the OVMF recipe always built an x86_64 firmware
regardless of the target architecture or target machine. This issue manifested
itself when qemu-system-i386 was used on an OVMF firmware image-- QEMU would
exit immediately rather than proceeding with the boot process.

The x86_64 firmware was unaffected by this issue.

Signed-off-by: Max Eliaser <max.eliaser@intel.com>