Silicon/SynQuacerPlatformFlashAccessLib: relax FV address check

In commit 913fdda9 ("Silicon/SynQuacerPlatformFlashAccessLib: don't
dereference FVB header fields"), we dropped all accesses to FVB header
field, which was necessary because the flash partition may not in fact
contain such a header. Instead, only an exact match on the base address
of the FV compared to the base address of the capsule payload would
result in a match, making it difficult to create capsules that only
update a subset of the flash contents.

Given that the FVB protocol provides a GetBlockSize() method that also
returns the number of consecutive blocks of that size, and does not rely
on the FVB header contents, we can actually infer the size of the flash
partition, and use it to decide whether a capsule payload targets an
area that is covered by this partition entirely.

This optimization allows us to extend the FV description to include the
SCP firmware partition without requiring us to actually provide a
payload for that partition immediately, which is useful as a preparatory
step.

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