mmc: Graceful fallback for fancy features

MMC high-speed, wide bus support and SD high-speed
are functions that aren't critical for correct
operation of the card. As such, they shouldn't mark
the card as bad or dead when there is a failure
activating these features.

This is needed in particular on some really stupid
hardware (e.g. Winbond's) where not all data transfer
commands are supported.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>