ArmPlatformPkg/MemoryInitPeiLib: reserve rather than remove FV memory

ArmPlatformPkg/MemoryInitPeiLib: reserve rather than remove FV memory

Instead of completely removing the memory occupied by the primary PrePi
FV from the memory map, thereby making it inaccessible to the OS, mark
it as boot services data. This will ensure that the memory is left
untouched by the firmware, but will release it to the OS when it calls
ExitBootServices().

Note that for reasons that are not entirely clear, this only works as
desired if the memory allocation HOB and the resource descriptor HOB
that describe the region are identical in offset and size, and so we
still need to iterate over the descriptors and split them up.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>