SH: Try to reduce R0 live ranges

SH: Try to reduce R0 live ranges

Some move or extend patterns will make long R0 live ranges and could
confuse LRA.

gcc/ChangeLog:
	* config/sh/sh-protos.h
        (sh_satisfies_constraint_Sid_subreg_index): Declare.
	* config/sh/sh.cc (sh_satisfies_constraint_Sid_subreg_index):
	New function.
	* config/sh/sh.md (extend<mode>si2_short_mem_disp_z,
	*mov<mode>_store_mem_index, mov<mode>_store_mem_index):
	New insn and insn_and_split patterns.
	(extend<mode>si2, mov<mode>): Use them for LRA.