sh: shared mstp32 clock code

Add shared 32-bit module stop bit clock support.

Processor specific code can use SH_CLK_MSTP32()
to initialize module stop bit clocks, and then
use sh_clk_mstp32() for registration.

Hook up the shared 32-bit module stop bit code to sh7785.

Add shared code for 4-bit divisor clocks.

Hook up the shared 4-bit divisor clock code to sh7785.