Draft: asus-grouper & asus-tilapia: move to community

Nexus 7 WIFI and GSM (asus-grouper, tilapia) are both well supported and except fully operational GPS, Camera and 3D (which being actively worked on) work very well.

Multiple users currently use these tablets on daily basis, so I'd like to propose move them to community.

Supported variants (3) - grouper (PM269, E1565), tilapia (E1565). These should be all models available on a market.

[v2]

• after 10 months of hard work (of people working on mainlining tegra patches and developing on -next-grate), time to bring effort for community again
• added Netfilter framework (nftables) support to the kernel configuration

[v3]

• Automatic kernel updates is tested only on tilapia (E1565) which I possess.

[v4]

• reverted v3, since it's undoable for now, because missing BOOT partition detection
• removed CONFIG_CRYPTO_ARC4 since it's deprecated and unneeded by iwd (only consumer)