kernel: update kernel 3.18 to rc4

include/kernel-version.mk

target/linux/bcm53xx/config-3.18

...td-spi-nor-allow-NULL-as-spi_device_id-in-spi_nor_s.patch

...tches-3.18/403-mtd-spi-nor-refactor-wait-till-ready.patch

...td-bcm53xxspiflash-new-driver-for-SPI-flahes-on-Bro.patch

...td-bcm53xxspiflash-try-using-JEDEC-as-one-of-method.patch

...brcm47xx/patches-3.18/027-mtd-bcm47xxpart-get-nvram.patch

target/linux/generic/config-3.18

target/linux/generic/patches-3.18/204-module_strip.patch

target/linux/generic/patches-3.18/220-gc_sections.patch

target/linux/generic/patches-3.18/304-mips_disable_fpu.patch

...472-mtd-m25p80-add-support-for-Winbond-W25X05-flash.patch

.../linux/generic/patches-3.18/642-bridge_port_isolate.patch

...eric/patches-3.18/643-bridge_remove_ipv6_dependency.patch

...eneric/patches-3.18/645-bridge_multicast_to_unicast.patch

...linux/generic/patches-3.18/653-disable_netlink_trim.patch

target/linux/generic/patches-3.18/655-increase_skb_pad.patch

...generic/patches-3.18/656-skb_reduce_truesize-helper.patch

target/linux/generic/patches-3.18/721-phy_packets.patch

target/linux/generic/patches-3.18/863-gpiommc.patch