ShellPkg: BcfgDisplayDump(): enforce minimum size for Boot#### and co.

ShellPkg: BcfgDisplayDump(): enforce minimum size for Boot#### and co.

"3.1.1 Boot Manager Programming" in the UEFI 2.5 spec mandates that
Boot#### and similar options contain EFI_LOAD_OPTION structures. The
EFI_LOAD_OPTION structure encodes the fixed initial part of the payload,
and we can (and should) use it to enforce a minimum size for variable
contents.

This patch is meant as a safety improvement.

Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Ryan Harkin <ryan.harkin@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19710 6f19259b-4bc3-4df7-8a09-765794883524