mtd: spi-nor: add id/id_len for flash_info{}

This patch adds the id/id_len fields for flash_info{}, and rewrite the
INFO to fill them. And at last, we read out 6 bytes in the spi_nor_read_id(),
and we use these new fields to parse out the correct flash_info.

Signed-off-by: Huang Shijie <shijie.huang@intel.com>
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>