kernel: Rearrange for 1.8

In 1.8 we want to streamline the kernel build process. Basically we
currently have multiple copies of the kernel source floating around
and the copying/compression/decompression is painful.

Lets assume we have a kernel source per machine since in most cases
this is true (and we have a sysroot per machine anyway). Basically,
instead of extracting a source into WORKDIR, then copying to a sysroot,
we now set S to point straight at STAGING_DIR_KERNEL.

Anything using kernel source can then just point at it and use:

do_configure[depends] += "virtual/kernel:do_patch"

to depend on the kernel source being present. Note this is different
behaviour to DEPENDS += "virtual/kernel" which equates to
do_configure[depends] += "virtual/kernel:do_populate_sysroot".

Once we do this, we no longer need the copy operation in
do_populate_sysroot, in fact there is nothing to do there (yay).

The remaining part of the challenge is to kill off the horrible
do_install. This patch splits it off to a different class, the idea here
is to have a separate recipe which depends on the virtual/kernel:do_patch
and just installs and packages the source needed to build modules on
target into a specific package.

Right now this code is proof of concept. It builds kernels and kernel
modules. perf blows up in do_package with issues on finding the kernel
version which can probably be fixed by adding back the right bit of do_install,
and adding a dependency of do_package[depends] += "virtual/kernel:do_install"
to perf. The whole thing needs a good write up, the corner cases testing
and probably a good dose of cleanup to the remaining code.

(From OE-Core rev: 3b3f7e785e27990ba21bc7cd97289c826a9a95d1)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/linux-kernel-base.bbclass

@@ -1,5 +1,5 @@
 # parse kernel ABI version out of <linux/version.h>
-def get_kernelversion(p):
+def get_kernelversion_headers(p):
     import re
 
     fn = p + '/include/linux/utsrelease.h'
@@ -9,7 +9,6 @@ def get_kernelversion(p):
     if not os.path.isfile(fn):
         fn = p + '/include/linux/version.h'
 
-    import re
     try:
         f = open(fn, 'r')
     except IOError:
@@ -24,6 +23,16 @@ def get_kernelversion(p):
             return m.group(1)
     return None
 
+
+def get_kernelversion_file(p):
+    fn = p + '/kernel-abiversion'
+
+    try:
+        with open(fn, 'r') as f:
+            return f.readlines()[0].strip()
+    except IOError:
+        return None
+
 def linux_module_packages(s, d):
 	suffix = ""
 	return " ".join(map(lambda s: "kernel-module-%s%s" % (s.lower().replace('_', '-').replace('@', '+'), suffix), s.split()))