This patch is a rework of the mmc_extcsd command:

- Always print registers. Previously we never printed registers that
  were already present in an older version of the spec
- Put register names, access type and width into an array indexed by the
  register number
- Print multibyte registers only once with the resulting value, and not
  bytewise.

There's still more to cleanup, like for example we want to write
multibyte registers once with the complete value, not bytewise. Anyway,
this is a start.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>