sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

Switch the arm64 VM_MEMATTR_DEVICE to nGnRE

Move device memory to a weaker type. The new device memory type allows
the system to acknowledge a write to a device before the write has
completed. This is inline with VM_MEMATTR_DEVICE on armv6/armv7.

Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D38945

Add a way to map arm64 non-posted device memory

On arm64 we currently use a non-posted write for device memory, however
we should move to use posted writes. This is expected to work on most
hardware, however we will need to support a non-posted option for some
broken hardware.

Reviewed by: imp, manu, bcr (manpage)
Differential Revision: https://reviews.freebsd.org/D29722

Add support for arm64 nGnRE device memory

On arm64 we can select how strongly we order device memory. Currently
we use the strongest type of non-Gathering, non-Reordering, no Early
write acknowledgement. This is equivalent to VM_MEMATTR_SO in the 32-bit
arm code.

Create a new memory type to remove the no Early write acknowledgement
option to create a memory attribute that is equivalent to the arm
VM_MEMATTR_DEVICE.

Keep the the old nGnRnE memory as what we provide for VM_MEMATTR_DEVICE
until we can test nGnRE on more hardware. A method for dynamically
switching back may be needed as at least one vendor is known to have
broken nGnRE memory.

Sponsored by: Innovate UK

Add the VM_MEMATTR_WRITE_THROUGH memory type to arm64 and use it to support
VM_MEMATTR_WRITE_COMBINING in the kernel. This fixes a bug where Xorg would
use write back cached memory for its graphics buffers. This would produce
artifacts on the screen as cachelines were written to memory.

MFC after: 1 week
Sponsored by: DARPA, AFRL

Add the start of the arm64 machine headers. This is the subset needed to
start getting userland libraries building.

Reviewed by: imp
Sponsored by: The FreeBSD Foundation