arm64: add a std.aws config

[kevans]

Summary

Mostly to document basic harware present on the platform; knowing that
Graviton exposes an ns8250 uart alone is quite helpful.

Sponsored by: NetApp, Inc.
Sponsored by: Klara, Inc.

[cperciva]

I always use GENERIC in EC2, but this seems accurate as far as it goes. Maybe you want to throw in an explicit device nvme as well since that's what modern EC2 systems use? But (as with acpi) that's something people are likely to have anyway.

[kevans]

In D36776#834870, @cperciva wrote:

I always use GENERIC in EC2, but this seems accurate as far as it goes. Maybe you want to throw in an explicit device nvme as well since that's what modern EC2 systems use? But (as with acpi) that's something people are likely to have anyway.

IIRC, ideally we include things here that *aren't* in std.arm64 or std.dev, even if they are in some of the other std.* SoC configs. Modulo the NVME_USE_NVD=0 line, which I realize now needs to go away because we have that in std.dev anyways, the bare minimum kernel config for ec2 (should this have been std.ec2 instead?) would be:

cpu        ARM64
ident     GRAVITON

include    "std.arm64"
include    "std.dev"
include    "std.aws"

(Tested to work, too, with exception to an FDT dependency that crept in to mmc bits via regulator headers that I'll work on separately)