atheros: remove linux 3.8 support

target/linux/atheros/config-3.8

...inux/atheros/patches-3.8/001-get_c0_compare_int_fix.patch

target/linux/atheros/patches-3.8/100-board.patch

.../linux/atheros/patches-3.8/101-early-printk-support.patch

target/linux/atheros/patches-3.8/105-ar2315_pci.patch

target/linux/atheros/patches-3.8/110-ar2313_ethernet.patch

target/linux/atheros/patches-3.8/120-spiflash.patch

target/linux/atheros/patches-3.8/130-watchdog.patch

...t/linux/atheros/patches-3.8/140-redboot_boardconfig.patch

...inux/atheros/patches-3.8/141-redboot_partition_scan.patch

...eros/patches-3.8/142-redboot_various_erase_size_fix.patch

target/linux/atheros/patches-3.8/210-reset_button.patch

...inux/atheros/patches-3.8/220-enet_micrel_workaround.patch