fs/ext4/ext4fs.c, fs/fs.c fs/fat/fat_write.c: Adjust 64bit math methods

The changes to introduce loff_t into filesize means that we need to do
64bit math on 32bit platforms.  Make sure we use the right wrappers for
these operations.

Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Suriyan Ramasami <suriyan.r@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@ti.com>
Tested-by: Pierre Aubert <p.aubert@staubli.com>