Move meta-rt recipes to oe-core (meta)

Keeping the rt recipes in their own layer has led to maintenance issues,
particularly with the linux-yocto-rt recipes. As these kernel types are part of
the same linux-yocto source repository, it seems reasonable to include the rt
kernel recipes alongside the standard recipes. A new recipes-rt directory for
the other recipes provides adequate separation and eliminates the need for a
separate layer.

As there is no meta-rt/conf/layer.conf to force the kernel, users must now
specify the rt kernel in their local.conf or in the machine.conf:

PREFERRED_PROVIDER_virtual/kernel = "linux-yocto-rt"

The merging of the rt recipes into the core also eliminates complications with
multiple layer dependencies for new BSP layers. Having to either separate RT
BSPs from standard BSPs or force users to add meta-rt to bblayers even when not
building an RT BSP (because the RT BSPs in the same layer would fail to parse
without it) was sub-optimal at best.

(From OE-Core rev: bafaaad264fe3e745c714951ddcf2784d33b755a)

Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-rt/conf/layer.conf

@@ -1,18 +0,0 @@
-# Default to first disk/first partition
-RSP_ROOT ?= "sda1"
-
-# We have a conf and classes directory, add to BBPATH
-BBPATH := "${BBPATH}:${LAYERDIR}"
-
-# We have an images and various recipe-* directories, add to BBFILES
-BBFILES := "${BBFILES} ${LAYERDIR}/images/*.bb ${LAYERDIR}/images/*.bbappend \
-            ${LAYERDIR}/recipes-*/*/*.bb ${LAYERDIR}/recipes-*/*/*.bbappend"
-
-BBFILE_COLLECTIONS += "rt"
-BBFILE_PATTERN_rt := "^${LAYERDIR}/"
-BBFILE_PRIORITY_rt = "8"
-
-# This layer builds images using a PREEMPT_RT kernel. Override any machine
-# specified kernel providers and leave it up to the kernel recipe to 
-# determine COMPATIBLE_MACHINE.
-PREFERRED_PROVIDER_virtual/kernel = "linux-yocto-rt"