Remove AVR32 patches from kernel-headers directory and put them in

"target/device/Atmel/arch-avre/kernel-headers-2.6.28.2"

Make sure BR2_KERNEL_HEADERS_PATCH_DIR is enabled for 2.6.28
Set
KERNEL_HEADERS_PATCH_DIR="target/device/Atmel/arch-avre/kernel-headers-2.6.28.2"
for Atmel AVR32 targets and "valka"