watchdog: ux500_wdt: Drop platform data

Drop the platform data passing from the PRCMU driver. This platform
data was part of the ambition to support more SoCs, which in turn
were never mass produced.

Only a name remains of the MFD cell so switch to MFD_CELL_NAME().

Cc: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20210922230947.1864357-1-linus.walleij@linaro.org
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>