fs/partitions/msdos: add support for large disks

In order to use disks larger than 2TiB on Windows XP, it is necessary to
use 4096-byte logical sectors in an MBR.

Although the kernel storage and functions called from msdos.c used
"sector_t" internally, msdos.c still used u32 variables, which results in
the ability to handle XP-compatible large disks.

This patch changes the internal variables to "sector_t".

Daniel said: "In the near future, WD will be releasing products that need
this patch".

[hirofumi@mail.parknet.co.jp: tweaks and fix]
Signed-off-by: Daniel Taylor <daniel.taylor@wdc.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>