mtd: spi-nor: add macros related to MICRON flash

Some MICRON related macros in spi-nor domain were ST.
Rename entries related to STMicroelectronics under macro SNOR_MFR_ST.

Added entry of MFR Id for Micron flashes, 0x002C.

Signed-off-by: Yogesh Gaur <yogeshnarayan.gaur@nxp.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>