mtd: spi-nor: Introduce spi_nor_init_flags()

Used to initialize the NOR flags for settings that are not defined
in the JESD216 SFDP standard, thus can not be retrieved when parsing
SFDP.
This moves the setting of SNOR_F_READY_XSR_RDY and SNOR_F_HAS_LOCK
late in the init call, without any functional change expected.
The rest of the flags were already set after the spi_nor_init_params().

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20211207140254.87681-8-tudor.ambarus@microchip.com