BaseTools/GenFv: optimize away redundant padding

BaseTools/GenFv: optimize away redundant padding

To prevent double padding of XIP modules leading to excessive
waste of FV space, try to adjust existing padding rather than
adding more.

Instead of adding a pad file to the FV to line up an FFS file that
itself may contain padding to line up the payload, try to find a
dedicated padding section inside the FFS, and reduce its size to
place all subsequent aligned FFS section at their respective minimum
alignments.

When using 4 KB section alignment (which is required on AARCH64 in
some cases), this will save 4 KB for each XIP module.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Yingke Liu <yingke.d.liu@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18080 6f19259b-4bc3-4df7-8a09-765794883524