[bootloader] Ignore buffers we didn't allocate

When the EFI network services are shared, buffers returned by
SimpleNetworkProtocol->GetStatus may not be ones we've allocated.
When this happens, just ignore them.

ZX-1516

Change-Id: I05a4b2d8766a41fbb2b88f3f4c6862b80d02d033

[zx] Rename bug references from MG-nnn to ZX-nnn

Change-Id: I07b0ee32bd7e8cc08e344896352c156b3b420349

[bootloader] Fix transmit buffer corruption.

MG-759
Unless we have transmissions pending, the UEFI simple network
protocol's GetStatus tx_buf parameter is unreliable, so don't
call it otherwise.

Change-Id: I2076d1735fbca0b34fa5ab56f7a08ed13353cf4f

[bootloader] commandline processing overhaul

- maintain a single central commandline
- simplify interface to this commandline
- ensure that later additions to the commandline
correctly override same-named existing entries
- split legacy boot path into its own file
- bump bootloader version
- display bootloader version next to bootloader name
- disable some debug chatter, declutter things a bit

Change-Id: I86e10bddd156089582bcb079018e5bb780cbbf24

[bootserver][bootloader] Faster netboot

Requires updating bootloader on devices

Change-Id: I084e737d7255348f6cf4bcf7ecf1721c632fd689

[bootloader] Fix printf warnings under Clang

This cleans up the printf formats in bootloader/ to use the
PRIx64 macro from <inttypes.h> rather than presuming that
uint64_t is unsigned long. (In Clang for the Windows target used
for the booloader, it's unsigned long long instead.)

It also fixes the makefiles so that 'make gigaboot' works.

Change-Id: I98de7c4c9abe429d101a9cc7f0c06767e8a72bfd

[bootloader] utils.h becomes xefi.h, helper functions renamed

Change-Id: I395ce58f9272b4b6cea4dd9103acf1938737e2af

[bootloader] Initial import of gigaboot

Original source:
https://fuchsia.googlesource.com/gigaboot20x6/
Upstream commit:
80eef665f1e248eafe48f9b430fdae702ece20c1

Change-Id: I1be9ad20831e0d790937446febc28755943884a5