meta-agl-bsp: Make more and better use of WIC images

meta-agl-bsp: Make more and better use of WIC images

- When we are using a WIC image, we should compress it (xz), provide a
  sha256sum of the compressed image and provide a bmap file for the
  uncompressed image.
- Ensure that in these targets we are listing WIC as the
  AGL_EXTRA_IMAGE_FSTYPES to be used.
- Based on the Beaglebone example, add WIC support for dra7xx-evm.  The
  only change from Beaglebone is that we must also include uEnv.txt as
  this is what controls the DTB for the correct LCD.

Bug-AGL: SPEC-899
Change-Id: I3f310a2eb268a4aaa0d791dfaa68d7fee350e150
Tested-by: Matt Porter <mporter@konsulko.com> (dra7xx-evm)
Tested-by: Tom Rini <trini@konsulko.com> (Intel)
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/11161
Reviewed-by: Scott Murray <scott.murray@konsulko.com>
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-boot-test: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>