kernel: remove linux 4.0 support

target/linux/generic/config-4.0

...x/generic/patches-4.0/000-keep_initrafs_the_default.patch

target/linux/generic/patches-4.0/020-ssb_update.patch

target/linux/generic/patches-4.0/021-bcma-from-4.1.patch

target/linux/generic/patches-4.0/021-ssb_sprom.patch

target/linux/generic/patches-4.0/022-bcma-from-4.2.patch

.../generic/patches-4.0/050-backport_netfilter_rtcache.patch

...x/generic/patches-4.0/060-mips_decompressor_memmove.patch

...gmac-register-fixed-PHY-for-ARM-BCM470X-BCM5301X-ch.patch

...ches-4.0/071-bgmac-allow-enabling-on-ARCH_BCM_5301X.patch

...01-bgmac-fix-descriptor-frame-start-end-definitions.patch

...es-4.0/072-02-bgmac-implement-GRO-and-use-build_skb.patch

...s-4.0/072-03-bgmac-implement-scatter-gather-support.patch

...es-4.0/072-04-bgmac-simplify-tx-ring-index-handling.patch

...gmac-leave-interrupts-disabled-as-long-as-there-is-.patch

...2-06-bgmac-set-received-skb-headroom-to-NET_SKB_PAD.patch

...hes-4.0/072-07-bgmac-simplify-rx-DMA-error-handling.patch

...es-4.0/072-08-bgmac-add-check-for-oversized-packets.patch

.../072-09-bgmac-increase-rx-ring-size-from-511-to-512.patch

.../patches-4.0/072-10-bgmac-simplify-dma-init-cleanup.patch