mmc: add packed command feature of eMMC4.5

This patch adds packed command feature of eMMC4.5.
The maximum number for packing read(or write) is offered
and exception event relevant to packed command which is
used for error handling is enabled. If host wants to use
this feature, MMC_CAP2_PACKED_CMD should be set.

Change-Id: Ieff82abf3250edf2c6d1e496decb24371fc7cf9f
Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
Reviewed-by: Maya Erez <merez@codeaurora.org>
Reviewed-by: Subhash Jadavani <subhashj@codeaurora.org>
Reviewed-by: Namjae Jeon <linkinjeon@gmail.com>
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>