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>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
meta-luv: ovmf: bump SVN revision for OVMF to 15699

This SVN revision has a fix for build failures under GCC 4.9 for x86_64
targets. This will ease eventual upstreaming of the OVMF recipe to Yocto
master, which uses GCC 4.9.

The bug is described on the EDK2 mailing list here:
http://www.mail-archive.com/edk2-devel@lists.sourceforge.net/msg07451.html
GCC 4.9 changed an alignment from 32 bytes to 64 bytes when building for a 64-
bit target, whereas OVMF was built with the expectation that the alignment
would be 32 bytes. This mismatch caused a build failure that looked like this:
 GenFw: ERROR 3000: Invalid
 Unsupported section alignment.

SVN revision 15699 of EDK2 includes a fix for this issue by the upstream EDK2
developers. When compiling with GCC 4.9 for a 64-bit target, the build OVMF
build configuration now anticipates a 64-byte alignment.

Signed-off-by: Max Eliaser <max.eliaser@intel.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>