meta-agl-bsp: restore wic disk images for qemux86-64

meta-agl-bsp: restore wic disk images for qemux86-64

The cleanup done in commit de577de9 ("Consolidation of
AGL_DEFAULT_IMAGE_FSTYPES after review of machine use") inadvertently
removed the wic.{xz,bmap} additions that were done in commit cdbe6578
("Extend qemux86-64 images to support real hardware").  Add them to
AGL_EXTRA_IMAGE_FSTYPES for qemux86-64 so that they will be available
for use on physical hardware again.

Bug-AGL: SPEC-2931

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I7ea9cc195add6d015390c7b2b359234f0bfeaaea