MdeModulePkg/DiskIo: Introduced 'PcdDiskIoDataBufferBlockNum'

PcdDiskIoDataBufferBlockNum replaced the hardcoded value into
the Disk I/O driver.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
Reviewed-By: Tian, Feng <feng.tian@intel.com>



git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15235 6f19259b-4bc3-4df7-8a09-765794883524