We make these two functions take a size_t pointer to how much space
was used on NAND to read or write the buffer (when reads/writes happen)
so that bad blocks can be accounted for.  We also make them take an
loff_t limit on how much data can be read or written.  This means that
we can now catch the case of when writing to a partition would exceed
the partition size due to bad blocks.  To do this we also need to make
check_skip_len count not just complete blocks used but partial ones as
well.  All callers of nand_(read|write)_skip_bad are adjusted to call
these with the most sensible limits available.

The changes were started by Pantelis and finished by Tom.

Signed-off-by: Pantelis Antoniou <panto@antoniou-consulting.com>
Signed-off-by: Tom Rini <trini@ti.com>