mtd: nand: Clarify Kconfig entry for software Hamming ECC entries

The software Hamming ECC correction implementation is referred as
MTD_NAND_ECC which is too generic. Rename it
MTD_NAND_ECC_SW_HAMMING. Also rename MTD_NAND_ECC_SMC which is an
SMC quirk in the Hamming implementation as
MTD_NAND_ECC_SW_HAMMING_SMC.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>