fix(package.accept_keywords) add ~amd64 to efitools and gnu-efi

This is required for these packages to build as upstream has not
stabilized them yet, and it's doubtful that will happen any year soon...
Merge pull request #189 from gregkh/sbsigntool-fork

fix(app-crypt/sbsigntool) fix cross-build for sbsigntool
fix(package.accept_keywords) put back ChromiumOS copyright.

I was wrong to remove it, oops.
fix(sys-kernel/coreos-kernel): Add assorted SCSI adapters for VMware.

VMware can emulate buslogic, lsilogic, and its own pvscsi adapters.
Build the whole lot of related devices into the kernel to ensure CoreOS
boots on any of them.
Merge pull request #191 from marineam/scsi

fix(sys-kernel/coreos-kernel): Add assorted SCSI adapters for VMware.
Merge pull request #190 from gregkh/new_keywords

fix(package.accept_keywords) add ~amd64 to efitools and gnu-efi
fix(coreos-base/hard-host-depends): add libtirpc

libtirpc is a build dependency for nfs-utils
feat(coreos-base/coreos): add nfs
Merge pull request #192 from philips/add-nfs

add NFS dependency to hard-host-deps