ARC: remove pinmux-ing

Signed-off-by: Frank Dols <frank.dols@synopsys.com>
ARC: remove gpio (not in use)

Signed-off-by: Frank Dols <frank.dols@synopsys.com>
ARC: remove unused clk_set_...() functions

Signed-off-by: Frank Dols <frank.dols@synopsys.com>
ARC: we do not support romboot

Signed-off-by: Frank Dols <frank.dols@synopsys.com>