MdeModulePkg: Add PROMPT&HELP string of pcd to UNI file
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Leo Duran <leo.duran@amd.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>