ARM: at91: Convert SPL_GENERATE_ATMEL_PMECC_HEADER to Kconfig

ARM: at91: Convert SPL_GENERATE_ATMEL_PMECC_HEADER to Kconfig

This commit converts the following items to Kconfig:

CONFIG_ATMEL_NAND_HWECC
CONFIG_ATMEL_NAND_HW_PMECC
CONFIG_PMECC_CAP
CONFIG_PMECC_SECTOR_SIZE
CONFIG_SPL_GENERATE_ATMEL_PMECC_HEADER

[PMECC References]
https://www.at91.com/linux4sam/bin/view/Linux4SAM/PmeccConfigure
https://www.at91.com/linux4sam/bin/view/Linux4SAM/AT91Bootstrap

[Mailing List Thread]
https://lists.denx.de/pipermail/u-boot/2018-December/350666.html

Fixes: 576471bd ("configs: at91: Remove CONFIG_SYS_EXTRA_OPTIONS assignment")
[trini: Make the migration be size neutral and possibly not fix the
above in all cases]
Reported-by: Daniel Evans <photonthunder@gmail.com>
Cc: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Derald D. Woods <woods.technical@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>