[meta-freescale] Adding -rt support for kernel

[Eric Nelson]

Hi all,

Based on some customer requests, we've applied the "-rt" patches
to our kernel trees and pushed branches like this to our Github
tree:
	https://github.com/boundarydevices/linux-imx6/tree/boundary-imx_3.10.17_1.0.0_ga-rt

This makes it pretty simple for someone who's used git to build
these kernels outside of Yocto, but is painful for integration
into a Yocto-based build.

For the "linux-imx" kernel, the package "linux-imx-rt" recipe
defines a new variant of the kernel, but I don't understand how
this can be used in a build.

In other words, do you specify
	PREFERRED_PROVIDER_virtual/kernel="linux-imx-rt"
or
	PREFERRED_VERSION_virtual/kernel_linux-imx="rt-3.10.17"

Please advise,


Eric