cubieboard2: added network kernel module as essential dependency

Adding sunxi_emac network driver as recommended *essential* machine dependency, rather than recommended *extra* dependency, to make sure it is included, even if packagegroup-base is not included.

See also https://www.yoctoproject.org/docs/current/ref-manual/ref-manual.html#var-MACHINE_EXTRA_RDEPENDS

Also removed kernel26, as this is deprecated, see http://www.openembedded.org/wiki/Migrating_metadata_to_OE-Core
linux_3.4: added cubieboard2 support
sunxi-board-fex: added cubieboard2 support
Updated based on latest sun7i-defconfig from jwrdegoede

URL:https://github.com/jwrdegoede/linux-sunxi/blob/sunxi-3.4/arch/arm/configs/sun7i_defconfig

Also enabled CONFIG_VFPv3
Added config file for avahi-daemon

Without this config file, avahi-daemon would not startup because of "Failed to create server: No suitable network protocol available" error, which is fixed by following configuration setting in /etc/avahi/avahi-daemon.conf:
disallow-other-stacks=yes
sdcard_image-a10: added fex support for cubieboard2
sdcard_image-a10: removed u-boot.bin - replaced by u-boot-sunxi-with-spl.bin
sunxi-board-fex: fixed typo in COMPATIBLE_MACHINE
sdcard_image-a10: fixed file existance test for script.bin
Merge pull request #5 from KristofRobot/cubieboard2

Cubieboard2 enhancements