mfd: ab8500-sysctrl: AB8505 doesn't have SYSCLKREQ5..8

So we're removing support for it.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Tested-by: Marcus COOPER <marcus.xm.cooper@stericsson.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>