nandwrite: unified reading from standard input and from file - part 3

nandwrite: unified reading from standard input and from file - part 3

Nandwrite tries to use lseek() when failing to write on a page. lseek()
will fail when used on the standard input so nandwrite fails. This code
replaces lseek with a buffer.

When the data is read, it is put in a buffer (filebuf). This buffer is
reset at each block boundary. So a "seek" just means reading from the
beginning of the buffer. writebuf and oobreadbuf are now just pointers
to locations in filebuf.

Signed-off-by: Jehan Bing <jehan@orb.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>