sdhci-of: reorganize driver to support additional hardware

This patch breaks down sdhci-of into a core portion and a eSDHC portion,
clearing the path to easily support additional hardware using the same OF
driver.

Signed-off-by: Albert Herranz <albert_herranz@yahoo.es>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>