RISC-V: update docs for -mpriv-spec/--with-priv-spec for 1.12

RISC-V: update docs for -mpriv-spec/--with-priv-spec for 1.12

While support for the privileged spec was added in a63375ac337
("RISC-V: Hypervisor ext: support Privileged Spec 1.12"), the
documentation has not been updated.  Add 1.12 to the relevant
documentation.

References: a63375ac337 ("RISC-V: Hypervisor ext: support Privileged Spec 1.12")

gas/ChangeLog:

	* config/tc-riscv.c: Add 1.12 to the usage message.
	* configure: Regenerate.
	* configure.ac: Add 1.12 to the help/usage message.
	* po/fr.po: Same.
	* po/ru.po: Same.
	* po/uk.po: Same.