arm: mxs: fix register definitions for clkctrl_gpmi and clkctrl_sspX

I tried clearing a bit by writing to hw_clkctrl_gpmi_clr, then
busy-waiting for it to actually clear. My board hung. The data sheet
agrees, these registers do not have _set, _clr, _tog, so fix up the
definitions. git grep -E 'clkctrl_(gpmi|ssp[0-9])_' says that nobody
uses those non-existing ops registers.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>