mtd: spi-nor: Move erase_map to 'struct spi_nor_flash_parameter'

All flash parameters and settings should reside inside
'struct spi_nor_flash_parameter'. Move the SMPT parsed erase map
from 'struct spi_nor' to 'struct spi_nor_flash_parameter'.

Please note that there is a roll-back mechanism for the flash
parameter and settings, for cases when SFDP parser fails. The SFDP
parser receives a Stack allocated copy of nor->params, called
sfdp_params, and uses it to retrieve the serial flash discoverable
parameters. JESD216 SFDP is a standard and has a higher priority
than the default initialized flash parameters, so will overwrite the
sfdp_params data when needed. All SFDP code uses the local copy of
nor->params, that will overwrite it in the end, if the parser succeds.

Saving and restoring the nor->params.erase_map is no longer needed,
since the SFDP code does not touch it.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>