[PATCH v2 2/2] RISC-V: Add Tenstorrent Ascalon 8 wide architecture

This adds the Tenstorrent Ascalon 8 wide architecture (tt-ascalon-d8)
to the list of known cores.

gcc/ChangeLog:

	* config/riscv/riscv-cores.def: Add tt-ascalon-d8.
	* config/riscv/riscv.cc (tt_ascalon_d8_tune_info): New.
	* doc/invoke.texi (RISC-V): Add tt-ascalon-d8 to -mcpu.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/mcpu-tt-ascalon-d8.c: New test.