mtd: Update MTD infrastructure to support 64bit device size

This patch brings the U-Boot MTD infrastructure in sync with the current
Linux MTD version (2.6.30-rc3). Biggest change is the 64bit device size
support and a resync of the mtdpart.c file which has seen multiple fixes
meanwhile.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Kyungmin Park <kmpark@infradead.org>