ShellPkg: Increase reallocation size for temp memory files

ShellPkg: Increase reallocation size for temp memory files

If data of any real size were to be piped from one command to another,
an inordinate amount of time could be taken up by reallocating memory
that is only 10 bytes bigger than what is currently needed. Also, this
could cause unwelcome memory fragmentation.

Added a define to control how much memory is reallocated beyond that
which is currently needed. Set it to 1K vs. the original 10 bytes.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jim Dailey <jim_dailey@dell.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>