Variable PEIM use to PCD entry to get the base address of NV Storegae region.

Variable PEIM use to PCD entry to get the base address of NV Storegae region.
This patch changes:

1) make the PcdFlashNvStorageVariableBase PCD entry type in Variable PEIM to be "DYNAMIC", which means it can be flexible to be FIX_AT_BUILD, DYNAMIC or PATCH_IN_MODULE.
2) make FlashMap depends on PCD_PPI
3) make FlashMap PEIM to the value of PcdFlashNvStorageVariableBase according NT emulator's FwhPPI installed by NT32 emulator's SEC.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@1223 6f19259b-4bc3-4df7-8a09-765794883524