MdePkg/Include: Definitions of EFI REST EX Protocol

MdePkg/Include: Definitions of EFI REST EX Protocol

Add definitions of EFI REST EX Protocol according
to UEFI spec v2.8 Section 29.7.2 EFI REST EX Protocol.

Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Signed-off-by: Siyuan Fu <siyuan.fu@intel.com>
Signed-off-by: Fan Wang <fan.wang@intel.com>
Signed-off-by: Abner Chang <abner.chang@hpe.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Nickle Wang <nickle.wang@hpe.com>
Reviewed-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>