configs: at91: Fix wrong definitions for CONFIG_PMECC_CAP

When CONFIG_ATMEL_NAND_HW_PMECC is set, CONFIG_PMECC_CAP defaults
to the value of 2. At the conversion to Kconfig for the PMECC config
values, some boards/defconfigs were wrongly configured.
Update CONFIG_PMECC_CAP to the PMECC_CAP value before the conversion.

Fixes: 49ad4029 ("ARM: at91: Convert SPL_GENERATE_ATMEL_PMECC_HEADER to Kconfig")
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>