Convert mci_of_parse into mci_of_parse_node, a function that takes
explicit deivce tree node pointer to be used for SD/MMC related
properties extraction. Implement original mci_of_parse as a wrapper
around the call to new function.

This is useful for controllers who specify parameter like bus witdth and
GPIOs as a part of main controller's child nodes (e.g. AT91 SoCs).

Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>