mmc: card: Add eMMC4.5 write packed commands unit-tests

Expose the following packed commands tests:
- Test the write packed commands list preparation
- Simulate a returned error code
- Send an invalid packed command to the card

Change-Id: I9e061a1992cc09f3203d25eba14418d9ebde371a
Signed-off-by: Lee Susman <lsusman@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>