spi: dw: Discard redundant DW SSI Frame Formats enumeration

spi: dw: Discard redundant DW SSI Frame Formats enumeration

The dw_ssi_type enumeration describes the SPI frame formats the controller
supports, like Motorola SPI, Texas Instruments SSP and National
Semiconductors Microwire, that is the serial protocol utilized for the
SPI-transfers. Depending on the DW SSI IP-core configuration the protocol
could be either fixed or selectable. If it is changebale the protocol can
be selected by means of the CTRL0.FRF field, which possible values encoded
by the dw_ssi_type enumeration.  Aside with the denoted enum the field
values are also described by a set of SPI_FRF_{SPI,SSP,MICROWIRE} macros.
Thus currently the DW SPI driver has got two entities describing the same
data. Let's get rid of the enumeration one then, since first it hasn't
been used as enumeration-type but merely as a parametrized values set and
second that would unify the macro-based CSR read/write interface of the
driver. While at it convert the macro names to be more descriptive about
the protocols they represent.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20211115181917.7521-3-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Mark Brown <broonie@kernel.org>