MdeModulePkg ScsiDiskDxe: Modify FlushBlocksEx() to follow UEFI spec

MdeModulePkg ScsiDiskDxe: Modify FlushBlocksEx() to follow UEFI spec

The function ScsiDiskFlushBlocksEx() in ScsiDiskDxe/ScsiDisk.c originally
always returns EFI_SUCCESS, which is not aligned with the UEFI spec.

This commit adds addtional checks to see if the media in the device is
changed or removed. Check for whether the device can be written is also
added. Corresponding status will be returned according to the check
result.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19444 6f19259b-4bc3-4df7-8a09-765794883524