ArmVirtPkg: use 'auto' alignment and FIXED placement for XIP modules

Now that GenFw correctly propagates the minimum alignment of the ELF
input sections to the PE/COFF binary, we can simply select 'auto'
alignment in the FDF Rule section instead of tweaking it by hand.

Also add the FIXED FFS attribute to the module types that may execute
in place. This enables a newly added optimization in GenFfs that strips
redundant padding, preventing excessive waste of FV space if the section
alignment is considerable (i.e., 2 KB or 4 KB)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18122 6f19259b-4bc3-4df7-8a09-765794883524