mtd: nand: qcom: allocate BAM transaction

- The BAM transaction is the core data structure which will be used
  for all the data transfers in QPIC NAND. Since the core framework
  in nand_base.c is serializing all the NAND requests so allocating
  BAM transaction before every transfer will be overhead. The memory
  for it be allocated during probe time and before every transfer,
  it will be cleared.

- The BAM transaction contains the array of
  command and data scatter gather list and indexes. For
  every transfer, all the resource will be taken from BAM
  transaction.

- The size of the buffer used for BAM transactions
  is calculated based on the NAND device with the maximum page size,
  among all the devices connected to the
  controller.

Reviewed-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>