oxnas: drop support for kernel 4.1

target/linux/oxnas/config-4.1

...patches-4.1/010-arm_introduce-dma-fiq-irq-broadcast.patch

...nux/oxnas/patches-4.1/250-add-plxtech-vendor-prefix.patch

...inux/oxnas/patches-4.1/300-introduce-oxnas-platform.patch

target/linux/oxnas/patches-4.1/310-oxnas-clocksource.patch

target/linux/oxnas/patches-4.1/320-oxnas-irqchip.patch

target/linux/oxnas/patches-4.1/330-oxnas-pinctrl.patch

target/linux/oxnas/patches-4.1/340-oxnas-pcie.patch

target/linux/oxnas/patches-4.1/350-oxnas-reset.patch

target/linux/oxnas/patches-4.1/400-oxnas-nand.patch

target/linux/oxnas/patches-4.1/500-oxnas-sata.patch

target/linux/oxnas/patches-4.1/700-oxnas-dwmac.patch

target/linux/oxnas/patches-4.1/800-oxnas-ehci.patch

target/linux/oxnas/patches-4.1/900-more-boards.patch

...xnas/patches-4.1/996-ATAG_DTB_COMPAT_CMDLINE_MANGLE.patch

target/linux/oxnas/patches-4.1/999-libata-hacks.patch