Add sam9x5 support

Adds support for the AT91SAM9x5 family to the meta-atmel layer.  These changes include:
- Adding conditionals through all recipes in the layer for building either for the at91sam9x5 chipset or for the sama5 chipset.
- Added patch for U-Boot to modify the bootargs to look for the proper filesystem image name and to boot a device tree kernel.
- Tested support of USB ports, DBGU, USART0, USART3, NAND flash, Ethernet, RTC and watchdog on an AT91SAM9G25-EK.  Was not able to implement full support of the watchdog under the linux-3.6.9-at91 kernel.
- Added recipe for the linux-3.9-at91 kernel and made it the preferred kernel.  Verified all the previously mentioned peripherals and verified the watchdog works.
- Added a watchdog MACHINE_FEATURE.  Setting this feature enables the watchdog in the AT91Bootstrap, U-Boot, and adds the watchdog to the device tree.

KNOWN ISSUES:
- Have not tested the build with any other chipset than the AT91SAM9G25.  Have not tested any peripherals that were not already mentioned.