OvmfPkg: introduce 4MB flash image (mainly) for Windows HCK

The "Confirm64KilobytesOfUnauthenticatedVariableStorage" test case of the
Secure Boot Logo Test ("Microsoft.UefiSecureBootLogo.Tests") suite in the
Microsoft Hardware Certification Kit expects to be able to populate the
variable store up to roughly 64 KB, with a series of 1 KB sized,
unauthenticated variables. OVMF's current live varstore area is too small
for this: 56 KB.

Introduce the FD_SIZE_4MB build macro (equivalently, FD_SIZE_IN_KB=4096),
which

- enlarges the full flash image to 4MB -- QEMU supports up to 8MB, see
  FLASH_MAP_BASE_MIN in "hw/i386/pc_sysfw.c" --,

- inside that, grows the varstore area / pflash chip to 528 KB, and within
  it, the live area from 56 KB to 256 KB.

Importantly, a firmware binary built with -D FD_SIZE_4MB will *not* be
compatible with a variable store that originates from a variable store
template built *without* -D FD_SIZE_4MB. This is the reason for the large
increase, as every such change breaks compatibility between a new firmware
binary and old varstore files.

Enlarging the varstore does not impact the performance of normal
operations, as we keep the varstore block size 4KB. The performance of
reclaim is affected, but that is expected (since reclaim has to rework the
full live area). And, reclaim occurs proportionally less frequently.

While at it, the FVMAIN_COMPACT volume (with the compressed FFS file in
it) is also enlarged significantly, so that we have plenty of room for
future DXEFV (and perhaps PEIFV) increments -- DXEFV has been growing
steadily, and that increase shows through compression too. Right now the
PEIFV and DXEFV volumes need no resizing.

Here's a summary:

  Description                Compression type                Size [KB]
  -------------------------  -----------------  ----------------------
  Non-volatile data storage  open-coded binary    128 ->   528 ( +400)
                               data
    Variable store                                 56 ->   256 ( +200)
    Event log                                       4 ->     4 (   +0)
    Working block                                   4 ->     4 (   +0)
    Spare area                                     64 ->   264 ( +200)

  FVMAIN_COMPACT             uncompressed        1712 ->  3360 (+1648)
    FV FFS file              LZMA compressed
      PEIFV                  uncompressed         896 ->   896 (   +0)
        individual PEI       uncompressed
          modules
      DXEFV                  uncompressed       10240 -> 10240 (   +0)
        individual DXE       uncompressed
          modules

  SECFV                      uncompressed         208 ->   208 (   +0)
    SEC driver
    reset vector code

For now, the 2MB flash image remains the default.

Cc: Gary Ching-Pang Lin <glin@suse.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

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