mtd: rawnand: omap_gpmc: Reduce .bss usage

Allocate omap_ecclayout on the heap as we have
limited .bss space on AM64 R5 SPL configuration.

Reduces .bss usage by 2984 bytes.

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-By: Michael Trimarchi <michael@amarulasolutions.com>
Link: https://lore.kernel.org/all/20221011115012.6181-9-rogerq@kernel.org


Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>