PerformancePkg: Make Dp print help information with -? flag in Shell.

PerformancePkg: Make Dp print help information with -? flag in Shell.

Since Shell supports finding help information from resource section
of application image. We enhance the Dp to add help information
string. After the Dp are loaded in system the help string will
be stored in resource section of the application image.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qiu Shumin <shumin.qiu@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>