spi: fsl-espi: factor out fsl_espi_init_regs

The register initialization is the same in fsl_espi_probe and in
of_fsl_espi_resume. Therefore factor it out into fsl_espi_init_regs.

It was actually a bug that CSMODE_BEF and CSMODE_AFT were not set
in of_fsl_espi_resume. Seems like nobody ever used values other
than zero for these parameters.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>