spi: sh-msiof: Move register definitions to <linux/spi/sh_msiof.h>

Move the MSIOF register and register bit definitions from the MSIOF SPI
driver to the existing header file <linux/spi/sh_msiof.h>, so they can
be shared with the MSIOF I2S driver.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/066d1086973eb309006258484e9fe8138807e565.1747401908.git.geert+renesas@glider.be


Signed-off-by: Mark Brown <broonie@kernel.org>