Add .type and .size directives to riscv libgcc functions.

Add .type and .size directives to riscv libgcc functions.

	libgcc/
	* config/riscv/div.S: Use FUNC_* macros.
	* config/riscv/muldi3.S, config/riscv/multi3.S: Likewise
	* config/riscv/save-restore.S: Likewise.
	* config/riscv/riscv-asm.h: New.

From-SVN: r255521