mtd: spi-nor: Rename Quad Enable methods

Rename macronix_quad_enable() to a generic name:
spi_nor_sr1_bit6_quad_enable().

Prepend "spi_nor_" to "sr2_bit7_quad_enable". All SPI NOR generic
methods should be prepended by "spi_nor_".

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