mmc: core: 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: I8013970fc9d54da7d92b0aca2bb0746189b9825b
Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
Signed-off-by: Maya Erez <merez@codeaurora.org>