mmc: card: Add eMMC4.5 packing control unit-tests

Expose the packing control test.
Test the packing control feature under these scenarios:
- Packing expected: entering write packing state,
  staying in write packing state.
- Packing not expected: not entering write packing state
  when not supposed to.
- Mixed states: test the ability to shift from packing
  to no-packing and back, and the opposite.

Change-Id: I5a93df8b5b7c48d355c3cc881699a3f9592914e6
Signed-off-by: Lee Susman <lsusman@codeaurora.org>
(cherry picked from commit 202befb5a5a344f88a0b4fd1ed07b9a2c7ce4e3d)

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>