ShellPkg: increase available size for PcdShellFileOperationSize

Some storage subsystems benefit by having shell file operation sizes (affecting copy and type commands right now) larger than 2^16.  This patch changes the PcdShellFileOperationSize type to 32-bits.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Eugene Cohen <eugene@hp.com>
reviewed-by: Jaben Carsey <jaben.carsey@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14534 6f19259b-4bc3-4df7-8a09-765794883524