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loader.efi: efipart needs better support detecting nested partitions

Just as disks can have nested partitions, the same happens with cd devices,
so we need to detect device paths and make sure we will not mix the handles.

To address this:

we fetch handle array and create linked list of block devices.
we walk the list and detect parent devices and set children pd_parent.
for {fd, cd, hd}, we walk device list and pick up our devices and store to
corresponding list. We make sure we store parent device first.

For sorting we use 3 steps: We check for floppy, we check for cd and then
everything else must be hd.

In general, it seems the floppy devices have no parent.
CD can have both parents and children (multiple boot entries, partitions
from the hybrid disk image).

Tested by: cross+freebsd@distal.com on Cisco UCS systems, C200 series (C220M5, C240M4).
Also on MBP with UEFI 1.10

Reported by: Chriss Ross
MFC after: 1w
Differential Revision: https://reviews.freebsd.org/D22553

loader: add HTTP support using UEFI

Add support for an HTTP "network filesystem" using the UEFI's HTTP
stack.

This also supports HTTPS, but TianoCore EDK2 implementations currently
crash while fetching loader files.
Only IPv4 is supported at the moment. IPv6 support is planned for a
follow-up changeset.

Note that we include some headers from the TianoCore EDK II project in
stand/efi/include/Protocol verbatim, including links to the license instead
of including the full text because that's their preferred way of
communicating it, despite not being normal FreeBSD project practice.

Submitted by: scottph
Reviewed by: imp, bcran
Differential Revision: https://reviews.freebsd.org/D20643

Add UEFI definitions related to converting string to DEVICE_PATH

Add definitions from UEFI 2.7 Errata B standards doc for converting a
text string to a device path. Added clearly missing 'e' at the end of
Device to resolve mismatch in that document in
EFI_DEVICE_PATH_FROM_TEXT_PROTOCOL element names.

Differential Revision: https://reviews.freebsd.org/D19971

Define ADR subtype of ACPI type for a device path.

efi: Do not pad the efi devpath structure

This solve problem when booting with efi on armv7
Reviewed by: imp, tsoome
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D14415

Move sys/boot to stand. Fix all references to new location

Sponsored by: Netflix