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: I23a15f94571da3ff9553a342dc37e1a8de6827c6
Signed-off-by: Lee Susman <lsusman@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>