mmc: Improve tinification

Drop all the extra content from the MMC core, so that tiny MMC support
is really tiny, no fancy anything. That means the tiny MMC support does
only 1-bit transfers at default speed settings. Moreover, this patch
drops duplicate instance of struct mmc mmc_static, which wasted about
360 bytes. Furthermore, since MMC tiny supports only one controller
at all times, get rid of mallocating the ext csd backup and replace
it with static array. All in all, this patch saves ~4 kiB of bloat
from the MMC core, which on platforms with severe limitations can be
beneficial.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
[trini: Fixup checkpatch.pl style warnings]
Signed-off-by: Tom Rini <trini@konsulko.com>