SH: Fix cost estimation of mem load/store

SH: Fix cost estimation of mem load/store

For memory loads/stores (that contain a MEM rtx) sh_rtx_costs would wrongly
report a cost lower than 1 insn which is not accurate as it makes loads/stores
appear cheaper than simple arithmetic insns.  The cost of a load/store insn is
at least 1 insn plus the cost of the address expression (some addressing modes
can be considered more expensive than others due to additional constraints).

gcc/ChangeLog:

	PR target/113533
	* config/sh/sh.cc (sh_rtx_costs): Adjust cost estimation of MEM rtx
	to be always at least COST_N_INSNS (1).  Forward speed argument to
	sh_address_cost.

Co-authored-by: Roger Sayle <roger@nextmovesoftware.com>