mfd: dbx500: Remove any mention of the BML8580CLK

The platform which it pertains to is no longer supported and is actually
causing some confusion in the new common clock implementation. A recent
patch removed its use in the clock driver, let's take out the definitions
too.

Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>