include: mmc: Export sanitized mmc headers

Export sanitized mmc.h and core.h for userspace.

Change-Id: I3a6eadde2023d974b0ce260a77082b01d8ba0b5d
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
[subhashj@codeaurora.org: fixed trivial merge conflicts]
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
[xiaonian@codeaurora.org: fixed trivial merge conflicts,
squashed two commits into one]
Signed-off-by: Xiaonian Wang <xiaonian@codeaurora.org>