mmc_of_parse() adaptations, switch mvsdio to mmc_of_parse()

Hi,

RESEND V3:
- Dropped patches 9 and 10, they are part of linux-next already
NB: patch 7 as well, but I did not want to change the numbering

V3 changes:
- Patch 01/10: Added EPROBE_DEFER case to mmc_of_parse()
- Added Acked-By to (unmodified) patches 02 and 03.

V2 changes:
- Converted mvsdio to use mmc_of_parse()
- Adapted DTS files using mvsdio accordingly
- Changed mmc_of_parse() to return errors to the caller

While adding DT support for the Sheevaplugs by Globalscale Technologies (Kirkwood), it turned out that the DT binding of mvsdio lacked features to properly support the hardware (active high/low of CD and WP pins could not be described in DT).

This is standard functionality provided by the mmc_of_parse() helper function. However, mmc_of_parse() may allocate GPIO lines. If the allocation fails, it outputs an error, but does not return an error to its caller. Therefore, a proposal to handle errors in mmc_of_parse() is made. This also allows to handle the EPROBE_DEFER case when GPIO is not loaded yet.

The patch set is structured as follows:

1 Adapt mmc_of_parse() to return errors
2-6 Handle errors in current drivers using mmc_of_parse() (compile tested
only)
7-8 Convert mvsdio and respective dts files to mmc_of_parse() (tested on
kirkwood)