mtd: rawnand: omap_gpmc: Optimize NAND reads

mtd: rawnand: omap_gpmc: Optimize NAND reads

Rename omap_nand_read() to omap_nand_read_buf() to reflect
actual behaviour.

Use FIFO read address instead of raw read address for reads.

The GPMC automatically converts 32-bit/16-bit reads to NAND
device specific reads (8/16 bit). Use the largest possible
read granularity size for more efficient reads.

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Michael Trimarchi <michael@amarulasolutions.com>
Link: https://lore.kernel.org/all/20221011115012.6181-5-rogerq@kernel.org
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>