ShellPkg: Increase PcdShellFileOperationSize

ShellPkg: Increase PcdShellFileOperationSize

This improves performance for dumb filesystem drivers
as block sizes tend to be more 4KB size than 1000 bytes
size.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Brendan Jackman <Brendan.Jackman@arm.com>
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17976 6f19259b-4bc3-4df7-8a09-765794883524