mtd: spi-nor: Merge spansion Quad Enable methods

Merge
    spansion_no_read_cr_quad_enable()
    spansion_read_cr_quad_enable()
into
    spi_nor_sr2_bit1_quad_enable().

Reduce code duplication by introducing spi_nor_write_16bit_cr_and_check().
The Configuration Register contains bits that can be updated in future:
FREEZE, CMP. Provide a generic method that allows updating all bits
of the Configuration Register.

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