mtd: nand: consolidate redundant flash-based BBT flags

This patch works with the following three flags from two headers (nand.h
and bbm.h):
  (1) NAND_USE_FLASH_BBT (nand.h)
  (2) NAND_USE_FLASH_BBT_NO_OOB (nand.h)
  (3) NAND_BBT_NO_OOB (bbm.h)

These flags are all related and interdependent, yet they were in
different headers. Flag (2) is simply the combination of (1) and (3) and
can be eliminated.

This patch accomplishes the following:
  * eliminate NAND_USE_FLASH_BBT_NO_OOB (i.e., flag (2))
  * move NAND_USE_FLASH_BBT (i.e., flag (1)) to bbm.h

It's important to note that because (1) and (3) are now both found in
bbm.h, they should NOT be used in the "nand_chip.options" field.

I removed a small section from the mtdnand DocBook because it referes to
NAND_USE_FLASH_BBT in nand.h, which has been moved to bbm.h.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>