mtd: spi-nor: Rename "n25q512a" to "mt25qu512a (n25q512a)"

n25q512a was rebranded to mt25qu512a after its spin off from STM.
mt25qu512a is different only in terms of operating frequency, the
JEDEC id is the same as in n25q512a.

Dual reads are supported (0x3b, 0x3c), set the SPI_NOR_DUAL_READ flag.
4-byte opcodes are supported, set the SPI_NOR_4B_OPCODES flag.

Tested Single I/O and QUAD I/O mode on LS1046FRWY.

Signed-off-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Signed-off-by: Ashish Kumar <Ashish.Kumar@nxp.com>
Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>
[tudor.ambarus@microchip.com: rename entry to "mt25qu512a (n25q512a)",
reword commit message, order entry by size, drop comment as it looked
redundant]
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>