webos_prebuilt_binaries: Add a bbclass for prebuilt binaries

:Release Notes:
If what's fetched by the SRC_URI for a component contains one or more
prebuilt binaries (perhaps in addition to source), then its recipe must
inherit from this bbclass.

:Detailed Notes:
If prebuilt binaries are only available for some of the supported
MACHINE-s, the inheriting recipe must set WEBOS_PREBUILT_BINARIES_FOR to
a space separated list of MACHINEOVERRIDE values for which the binaries
are available. WEBOS_PREBUILT_BINARIES_FOR is processed into a value
for COMPATIBLE_MACHINE.

:Testing Performed:
Only build tested and checked with bitbake -e and bitbake -n.

:QA Notes:
No change in image.

:Issues Addressed:
[GF-13889] Invent a bbclass to specify components with prebuilt binaries

Open-webOS-DCO-1.0-Signed-off-by: Herb Kuta <herb.kuta@lge.com>
Change-Id: I1990444ccba76c9fbe63453eb382051e974eac48
Reviewed-on: https://g2g.palm.com/3133
Reviewed-by: Herb Kuta <herb.kuta@lge.com>
Tested-by: Herb Kuta <herb.kuta@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Susan Montooth <susan.montooth@lge.com>