yocto/[fvp-rd-kronos,linux]: Use linux-yocto for virtualization

This is a temporary commit which disables linux-yocto-rt for
virtualization, due to the following intermittent issue:
When trying to login into domu2 using "xl console domu2"
It returns "domu2 is an invalid domain identifier (rc=-6)"
Also  using "xl list" returns only domu1,
but when checking "/etc/xen/auto" you can find both domu1 and domu2.
Analysis indicate that this is caused by the linux-yocto-rt update
causing the Xen bus for Dom0 to fail.

Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Signed-off-by: Ziad Elhanafy <ziad.elhanafy@arm.com>