[meta-xilinx] Staged changes for meta-xilinx

[Nathan Rossi]

Hi All,

So I have been working on some changes to meta-xilinx around kernel configs, etc. I have not yet pushed them to master but am hoping to for this coming BSP release to coincide with 'dizzy'/1.7.

I have pushed the branch to my github repo as 'nrossi/next'.
https://github.com/nathanrossi/meta-xilinx/compare/nrossi/next

The major changes that I have made include.

Switching to use the linux-yocto and kernel-yocto.bbclass recipe infrastructure and kernel configuration management:
* This has been done for both linux-yocto and linux-xlnx within the meta-xilinx layer
* Existing configs have been split up and put in respective kernel config caches (xilinx-common, xilinx-machine and xilinx-base)
 * xilinx-common - The main source for Zynq and MicroBlaze baseline config fragments (e.g. common platform/soc/drivers/etc).
 * xilinx-machine - BSP/Machine specific config fragments, currently this is just MicroBlaze machines.
 * xilinx-base - The linux-xlnx defconfig converted into fragments such that is resembles what the default linux-yocto kernel cache provides.

Removing the MACHINE_KCONFIG variable and associated recipe code:
* To have per machine features, KERNEL_FEATURES is the variable that should be used

Device Trees are no longer compiled by the kernel (device-tree.bb):
* MACHINE_DEVICETREE is still used, but the intention is to retire it in favor of having bsp recipes that provide the device-tree
* KERNEL_DEVICETREE can now be used to build the kernel's device-trees if desired
* Currently the recipe generates uImage-<machine>.dtb, this is to make sure the qemu machines still work correctly via runqemu
  * This can be removed when the runqemu is changes in oe-core. Since oe-core is essentially in release state I will look at resolving this for the next release.

Additional clean-up/rev-up changes:
* Fixes to configs themselves
* Some dts changes to fix up probe issues/etc with various kernel versions

@Elvis: I will spin some patches to fix up any issues with the machines in the meta-xilinx-community layer when I go to push these changes into master.

Regards,
Nathan