Increase bit rate range for RSPI on legacy SH by making use of the Bit
Rate Frequency Division Setting field in Command Registers, just like is
already done on RZ/A.  This decreases the lower limit by a factor of 8.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200819125904.20938-5-geert+renesas@glider.beSigned-off-by: Mark Brown <broonie@kernel.org>