RISC-V: Update testcase comments to point to PSABI rather than Table A.6

RISC-V: Update testcase comments to point to PSABI rather than Table A.6

Table A.6 was originally the source of truth for the recommended mappings.
Point to the PSABI doc since the memory model mappings have been moved there.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/amo/a-rvwmo-fence.c: Replace A.6 reference with PSABI.
	* gcc.target/riscv/amo/a-rvwmo-load-acquire.c: Ditto.
	* gcc.target/riscv/amo/a-rvwmo-load-relaxed.c: Ditto.
	* gcc.target/riscv/amo/a-rvwmo-load-seq-cst.c: Ditto.
	* gcc.target/riscv/amo/a-rvwmo-store-compat-seq-cst.c: Ditto.
	* gcc.target/riscv/amo/a-rvwmo-store-relaxed.c: Ditto.
	* gcc.target/riscv/amo/a-rvwmo-store-release.c: Ditto.
	* gcc.target/riscv/amo/a-ztso-fence.c: Ditto.
	* gcc.target/riscv/amo/a-ztso-load-acquire.c: Ditto.
	* gcc.target/riscv/amo/a-ztso-load-relaxed.c: Ditto.
	* gcc.target/riscv/amo/a-ztso-load-seq-cst.c: Ditto.
	* gcc.target/riscv/amo/a-ztso-store-compat-seq-cst.c: Ditto.
	* gcc.target/riscv/amo/a-ztso-store-relaxed.c: Ditto.
	* gcc.target/riscv/amo/a-ztso-store-release.c: Ditto.
	* gcc.target/riscv/amo/zaamo-rvwmo-amo-add-int.c: Ditto.
	* gcc.target/riscv/amo/zaamo-ztso-amo-add-int.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-compare-exchange-int-acquire-release.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-compare-exchange-int-acquire.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-compare-exchange-int-consume.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-compare-exchange-int-relaxed.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-compare-exchange-int-release.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-compare-exchange-int-seq-cst-relaxed.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-compare-exchange-int-seq-cst.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-subword-amo-add-char-acq-rel.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-subword-amo-add-char-acquire.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-subword-amo-add-char-relaxed.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-subword-amo-add-char-release.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-subword-amo-add-char-seq-cst.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-compare-exchange-int-acquire-release.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-compare-exchange-int-acquire.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-compare-exchange-int-consume.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-compare-exchange-int-relaxed.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-compare-exchange-int-release.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-compare-exchange-int-seq-cst-relaxed.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-compare-exchange-int-seq-cst.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-subword-amo-add-char-acq-rel.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-subword-amo-add-char-acquire.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-subword-amo-add-char-relaxed.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-subword-amo-add-char-release.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-subword-amo-add-char-seq-cst.c: Ditto.

Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>