MdePkg DxePcdLib: Updates DxePcdLib instance comments.

Describe PCD service can't be used at Runtime phase.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>

(Sync patch r16403 from main trunk.)
(cherry picked from commit 5347e8d5c32bb359a7d04e232e5cd7293af4e0bb)

git-svn-id: svn://svn.code.sf.net/p/edk2/code/branches/UDK2014.SP1/MdePkg@16441 6f19259b-4bc3-4df7-8a09-765794883524
MdePkg/MdeModulePkg: Implement the missing SetMemorySpaceCapabilities function.

It is defined in the PI Specification version 1.3.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Eugene Cohen <eugene@hp.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

(Sync patch r16409 from main trunk.)

git-svn-id: svn://svn.code.sf.net/p/edk2/code/branches/UDK2014.SP1/MdePkg@16443 6f19259b-4bc3-4df7-8a09-765794883524