webos_kernel_dep.bbclass: Add virtual/kernel dependency

:Release Notes:
Add virtual/kernel dependency.

:Detailed Notes:

:Testing Performed:
Only build tested.

:QA Notes:
No change to image.

:Issues Addressed:
[ES-715] webos_kernel_dep.bbclass: Append virtual/kernel to DEPENDS

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I0d880a2ea7a604bbb58be05517bec4986bb40e3c
Originally-reviewed-on: https://gpro.palm.com/58819
Reviewed-on: https://g2g.palm.com/6426
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>