...and adaptation of the users of 'Block::Driver', 'Block::Root' and 'Block::Session_component' to the modified interface. Issue #1987
Merge the platform-specific files and classes (they merely aggregated themselves) so that each platform provides merely one class Sd_card::Driver. Also, the Sd_card::Driver_base class is introduced for the generic parts of Sd_card::Driver. Ref #2206