configs: at91: Fix the involuntarily disablement of NAND PMECC

SPL_GENERATE_ATMEL_PMECC_HEADER selects:
ATMEL_NAND_HWECC [=y] && ATMEL_NAND_HW_PMECC [=y].

With the removal of SPL_GENERATE_ATMEL_PMECC_HEADER,
ATMEL_NAND_HW_PMECC and ATMEL_NAND_HWECC were no longer
selected. Also, when the SPL_GENERATE_ATMEL_PMECC_HEADER was removed,
the configs were not updated using savedefconfig, thus the
'commit d168bcb6 ("configs: Resync with savedefconfig")'
further removes the CONFIG_PMECC_CAP value.

Update defconfigs and add CONFIG_ATMEL_NAND_HW_PMECC,
which selects ATMEL_NAND_HWECC, in order to restore NAND PMECC
support. Restore CONFIG_PMECC_CAP value.

Fixes: 57f76c2a ("configs: at91: remove SPL_GENERATE_ATMEL_PMECC_HEADER from non-nand configs")
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>