MdeModulePkg FaultTolerantWriteDxe: Remove assumptions below in FTW driver.

MdeModulePkg FaultTolerantWriteDxe: Remove assumptions below in FTW driver.
1. Work space and spare block must be in a FVB with FV header.
Updated to work space and spare block could be in independent FVBs that are without FV header.
2. NV region, work space and spare block must have same BlockSize.
Updated to NV region, work space and spare block could have different BlockSize.
3. Works space size must be <= one block size.
Update to work space size could be <= one block size (not span blocks) or > one block size (block size aligned).

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16201 6f19259b-4bc3-4df7-8a09-765794883524