mtd: spi-nor: add support for Cypress Semper flash

The Cypress Semper flash is an xSPI compliant octal DTR flash. Add
support for using it in octal DTR mode.

To avoid forward declarations, move spi_nor_set_read_settings() and
spi_nor_set_pp_settings() to the top.

This flash uses 2-bit ECC by default and in that mode we cannot do
partial page writes. The first partial write would work but any
subsequent writes won't. UBIFS makes such partial writes. As a result,
UBIFS is not fully functional and needs to be patched to respect the
write size for SPI NOR flashes.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>